Mohs micrographic surgery billing is the practice of reporting CPT codes 17311 through 17315 for one physician who both excises a skin cancer layer by layer and reads its pathology, so that every stage, tissue block, and repair is coded to the correct payer rule. It is one of the trickiest areas in dermatology coding, and getting it right is the difference between full first-pass payment and a stack of denials.
Mohs surgery billing is one of the trickiest areas in dermatology coding.
You’re not alone if you’ve ever stared at a claim for 17311 and wondered whether you should also bill a pathology code, or if using the -59 modifier was going to trigger a denial.
The good news is that once you understand the logic behind the CPT code family, it actually makes sense.
This guide walks you through exactly how to bill each stage, what goes where, and the traps that get practices in trouble.
What Makes Mohs Surgery Coding Different
Mohs micrographic surgery is unique in medicine because one physician acts in two distinct capacities: surgeon and pathologist.
The surgeon removes the tumor layer by layer, maps and color-codes the specimens, prepares the slides, and interprets them microscopically, all in one operative session.
Because this dual role is bundled into the Mohs codes, you cannot separately bill pathology codes (88300–88309, 88331–88332, 88342) when the Mohs surgeon performs the pathology.
Those pathology services are included in 17311–17315.
If a different physician (such as a separate pathologist) examines the slides, Mohs coding is not appropriate, you would use standard excision codes for the surgeon and separate pathology codes for the pathologist.
The 5 CPT Codes for Mohs Surgery
The Mohs code family is divided by anatomic site and stage/block count.
| CPT Code | Description | When to Use |
| 17311 | First stage, head/neck/hands/feet/genitalia, up to 5 tissue blocks | First layer on high-risk areas |
| +17312 | Each additional stage, head/neck/hands/feet/genitalia | Second, third, etc. stages on high-risk areas |
| 17313 | First stage, trunk/arms/legs, up to 5 tissue blocks | First layer on lower-risk areas |
| +17314 | Each additional stage, trunk/arms/legs | Second, third, etc. stages on lower-risk areas |
| +17315 | Each additional block after the first 5, any stage | When any single stage requires more than 5 blocks |
Codes 17311 and 17313 are primary, they stand alone for the first stage.
Codes 17312, 17314, and 17315 are add-on codes; they are never billed without a primary code on the same date of service.
All Mohs surgery codes are exempt from multiple procedure reduction.
This means you get full payment for each stage, no reduction for performing multiple stages on the same day.
Stage-by-Stage Billing Logic
First Stage
For the first layer of Mohs on a lesion, you bill either 17311 or 17313, depending on the anatomic site:
- 17311: Head (including scalp, face, nose, lips, eyelids, ears), neck, hands, feet, genitalia, or any location with surgery directly involving muscle, cartilage, bone, tendon, major nerves, or vessels
- 17313: Trunk, arms, or legs
The first-stage code includes the initial excision, mapping, color coding, tissue processing, slide preparation, and microscopic examination of up to 5 tissue blocks.
Additional Stages
For each subsequent layer after the first, bill either 17312 or 17314, matching the site grouping you used for the first stage:
- +17312: Additional stage on head/neck/hands/feet/genitalia
- +17314: Additional stage on trunk/arms/legs
You bill one add-on code per additional stage, not per block (up to 5 blocks per stage).
When a lesion needs several additional stages, do not write a separate claim line for each one. The additional-stage codes are totalled and reported as a single line with the correct number of units. Three stages on the trunk are 17313 once, then 17314 with two units on one line, not two separate 17314 lines. Splitting add-on stages across lines runs into Medically Unlikely Edit (MUE) limits and unit denials, which is one of the most common ways a clean Mohs case gets rejected.
Extra Blocks
If any single stage requires more than 5 tissue blocks, bill +17315 for each block beyond the first 5.
For example: A facial lesion’s first stage is divided into 7 tissue blocks. You bill 17311 (which includes the first 5 blocks), plus 17315 × 2 units (for the 6th and 7th blocks).
Critical documentation note: Code 17315 represents one piece of tissue mapped separately—not the number of slides cut from a block. Count blocks, not slides.
Billing Multiple Lesions on the Same Day
When you perform Mohs on more than one separate lesion during the same operative session, each lesion is billed on its own claim line with a -59 modifier.
Example: Two facial lesions requiring Mohs on the same day.
- Lesion 1, first stage: 17311
- Lesion 1, additional stages: 17312 (as many as needed)
- Lesion 2, first stage: 17311 -59 (separate line)
- Lesion 2, additional stages: 17312 -59 (separate lines)
The -59 modifier tells the payer this is a distinct, separate lesion—not just a continuation of the first one.
Some payers now prefer the more specific X{EPSU} modifiers over -59. When the second service is at a separate site, XS communicates a separate structure, and XU communicates an unusual non-overlapping service. The logic is identical to -59, but the X-modifier names the reason precisely, which several commercial payers and some Medicare contractors require. Check the payer policy and use XS or XU where the payer asks for it instead of -59.
The -59 Modifier Trap
The -59 modifier has a specific job in Mohs billing: identifying a separate lesion, not separating pathology services from Mohs.
Do NOT use -59 on the Mohs surgery codes themselves to indicate that pathology was performed. Pathology is bundled into the Mohs codes.
- Use -59 on the Mohs code line only when billing an additional distinct lesion.
- Do NOT use -59 on pathology codes (88300–88309, 88331–88332) for Mohs-related tissue—they’re included in 17311–17315 anyway.
Pathology Bundling and the Separate-Biopsy Exception
The pathology work in a Mohs case is already paid inside 17311 through 17315. When the Mohs surgeon maps, processes, and reads the slides, those services are bundled, and the surgical pathology codes 88300 through 88309, 88331 through 88332, and 88342 are not separately billable for the Mohs specimen. This bundling is enforced through the National Correct Coding Initiative (NCCI) edits, so a claim that adds a pathology code to the same specimen will hit a procedure-to-procedure edit and deny.
There is one real exception. If the surgeon takes a genuinely separate biopsy or excision at a different site that is not part of the Mohs specimen, that distinct service and its pathology can be reported, with a modifier to show it was separate. The test is simple: is the tissue part of the Mohs layer, or is it a different lesion at a different location. Only the second case supports a separate pathology charge. Do not append a modifier to a Mohs pathology code to try to unbundle it, because the bundling is by design, not by edit error.
Two-Day Mohs Surgeries
Sometimes a patient cannot tolerate the full procedure in one day, and additional stages are completed the following day.
Do not simply carry over the stage count. Computer edits will reject claims where 17312 appears without 17311 on the same date of service.
Correct approach:
- Day 1: Bill 17311 (first stage)
- Day 2: Bill 17312 (additional stage) and a new 17311? No. Actually, start with 17311 again on day two? Let’s be precise.
According to CMS, if Mohs on a single site cannot be completed on the same day and additional stages are performed the following day, you must start with the primary code (17311) on day two. Computer edits will reject a claim when a secondary code (17312) is billed without the primary code (17311) also appearing on the same date of service in the same claim.
Example:
- Day 1: Stage 1 completed → bill 17311
- Day 2: Stage 2 completed → bill 17311 (first stage on that date) AND 17312 (if there was a further stage on that day)
You need to re-read the CMS guidance carefully.
Actually, the official CMS guideline states: “If Mohs on a single site cannot be completed on the same day because the patient could not tolerate further surgery and the additional stages were completed the following day, you must start with the primary code (CPT code 17311) on day two. Computer edits will reject claims where a secondary code (e.g., CPT code 17312) is billed without the primary code (e.g., CPT code 17311) also appearing on the same date of service, same claim.”
This means:
- Day 1, Stage 1 (first layer): Bill 17311
- Day 2, Stage 2 (second layer): Bill 17311 (first stage on day two) + 17312 (if you do a third stage on day two)
- Day 2, Stage 2 ONLY (no third stage): Bill 17311 (first stage on day two)
But isn’t that double-billing a first stage? The logic is that on day two, the first Mohs layer of that session starts with 17311. The primary code resets each day the patient is brought to the OR.
- Alternative interpretation: Some experts recommend billing both days on the same claim form and reporting the date of service as the date the last stage was completed. Check your specific payer’s policy.
- The safest approach: Follow your payer’s specific guidelines for two-day Mohs and document clearly. Some payers allow you to report the entire procedure with the date of the last stage. When in doubt, call the payer’s provider relations line.
Billing Repairs After Mohs
Repairs (closure of the surgical defect after Mohs) are billed separately from the Mohs codes.
The repair codes depend on the complexity of the closure:
- Simple repair: 12001–12018 (based on wound length)
- Intermediate repair: 12031–12057
- Complex repair: 13100–13153
- Flaps and grafts: 14000–14302
Modifier -51 is typically appropriate for multiple procedures performed in the same session (Mohs + repair). Some payers require -51 on the repair code (the lesser procedure); others require it on the lower-valued code. Check your payer’s policy.
Documentation Requirements
Denied claims can be appealed, but only with proper documentation. Your operative note must clearly show:
- The Mohs technique was performed using accepted methods
- The same physician performed both surgery and pathology services
- The location, number, and size of the lesion(s)
- The number of stages performed
- The number of specimens per stage (document blocks, not slides)
A CLIA certification number on all claims for 17311–17315, submitted in Item 23 of the CMS 1500 form. This proves your facility is certified to perform the pathology component.
The Mohs stage codes carry a zero-day global period, which means there is no built-in follow-up window bundled into the procedure. If the patient has a separately identifiable evaluation and management service on the same day, for example a problem-oriented visit that goes beyond the decision to perform Mohs, that visit may be reported with modifier 25. The note must clearly support a service distinct from the procedure, or the E/M will be denied as part of the surgery.
2026 RVU and Payment Information
Mohs surgery is among the highest-productivity dermatology procedures. The figures below are office (non-facility, place of service 11) Medicare allowed amounts at the national unadjusted rate, since that is where the large majority of Mohs cases are billed. Hospital outpatient (facility) rates are lower because the practice expense shifts to the facility. Actual payment varies by GPCI locality and payer.
According to 2026 Medicare data:
| CPT Code | Description | wRVU | Approx. Medicare Payment* |
| 17311 | First stage, H/N/H/F/G | 14.68 | $480 |
| +17312 | Additional stage, H/N/H/F/G | 5.25 | $172 |
| 17313 | First stage, trunk/extremities | 12.61 | $413 |
| +17314 | Additional stage, trunk/extremities | 4.50 | $147 |
| +17315 | Each additional block beyond 5 | 0.74 | $24 |
*Using approximate 2026 conversion factor. Actual payment varies by geographic location.
Most Mohs cases average 1.5–2 stages. A typical two-stage facial Mohs (17311 + 17312) yields approximately 19.93 wRVU (~$652 for the Mohs portion alone, before repair fees).
Commercial Payer Differences
Medicare sets the baseline, but commercial payers do not all follow it. Three differences matter most for Mohs.
First, credentialing. Some commercial plans reimburse 17311 through 17315 only when the surgeon holds board certification in dermatology and a recognized Mohs subspecialty credential, such as completion of an ACGME or ACMS fellowship. A surgeon who is not credentialed for Mohs with that payer can see the entire claim denied regardless of how cleanly it is coded.
Second, prior authorization. A handful of commercial plans require prior authorization for Mohs on lower-risk sites or for certain tumor types, even though Medicare does not. Verify the requirement before the date of service, because retroactive authorization is rarely granted.
Third, modifier and unit rules. Commercial payers vary on whether they accept -59 or require an X-modifier, and on how they want multiple stages reported. Confirm each payer’s policy rather than assuming it mirrors Medicare.
The practical rule is to keep a short payer matrix for your top Mohs carriers that records their credentialing requirement, prior authorization stance, and modifier preference, and to verify any specific plan policy against its current published document before you rely on it.
Common Billing Errors to Avoid?
Error 1: Billing pathology separately
The pathology work (88300–88309, 88331–88332, 88342) is bundled into 17311–17315. Do not bill separately, even with -59, unless it’s for a completely unrelated biopsy at a different site.
Error 2: Incorrect stage count
Each stage (layer) is one unit of 17312 or 17314. Do not multiply by the number of blocks (unless using 17315 for blocks beyond 5).
Error 3: Using 17311 for a second lesion without -59
Multiple lesions require separate lines with -59. Otherwise, the payer may process it as one lesion with a typo.
Error 4: Billing add-on codes without primary codes
Codes 17312, 17314, and 17315 are add-ons. They cannot be billed without 17311 or 17313 on the same date of service.
Error 5: Missing CLIA number
All Mohs claims must include the CLIA certification number in Item 23. Without it, Medicare will reject the claim.
Error 6: Assuming all BCBS plans follow Medicare rules
Commercial payers often have different requirements. Blue Cross of Minnesota, for example, requires board certification in Dermatology and an active subspecialty certification in Mohs Micrographic Surgery for reimbursement of 17311–17315. Check each payer’s policy.
When to Use Each Code?
| Scenario | Codes to Bill |
| Facial lesion, 1 stage, 4 blocks | 17311 |
| Facial lesion, 2 stages, 4 blocks each | 17311 (stage 1) + 17312 (stage 2) |
| Trunk lesion, 1 stage, 4 blocks | 17313 |
| Trunk lesion, 3 stages, 4 blocks each | 17313 + 17314 (stage 2) + 17314 (stage 3) |
| Facial lesion, 1 stage, 7 blocks | 17311 + 17315 × 2 units |
| Facial lesion, 2 stages, 7 blocks in stage 1, 4 in stage 2 | 17311 + 17315 × 2 units + 17312 |
| Two facial lesions, 1 stage each, 4 blocks each | 17311 (lesion 1) + 17311 -59 (lesion 2) |
| Mohs + complex repair on face | 17311 + 13152 (complex repair code) |
Final Takeaway
Mohs billing is logical once you understand the “one physician, two roles” concept. The codes bundle surgery and pathology.
You bill by stage, not block (unless >5 blocks). Repairs are separate. Multiple lesions need -59. And always, always include your CLIA number.
Get these fundamentals right, and your Mohs claims will pay correctly. Get them wrong, and you’re looking at claim denials, appeals, and lost revenue.
Frequently Asked Questions
What CPT codes are used for Mohs surgery?
Mohs uses five codes, 17311 through 17315. Use 17311 for the first stage on the head, neck, hands, feet, or genitalia, and 17313 for the first stage on the trunk, arms, or legs. Add 17312 or 17314 for each additional stage, and 17315 for each tissue block beyond the first five in any single stage.
What is the difference between 17311 and 17313?
The difference is anatomy. 17311 covers the first Mohs stage on higher-risk sites: head, neck, hands, feet, genitalia, or any site involving muscle, cartilage, bone, tendon, major nerves, or vessels. 17313 covers the first stage on the trunk, arms, or legs. Match the additional-stage code, 17312 or 17314, to whichever first-stage code you used.
Can you bill pathology separately with Mohs surgery?
No. The pathology is bundled into 17311 through 17315 when the Mohs surgeon reads the slides, so codes like 88305 and 88331 are not separately payable for the Mohs specimen. The only exception is a genuinely separate biopsy or excision at a different site that is not part of the Mohs procedure.
How do you bill more than five tissue blocks in one stage?
Bill 17315 for each block beyond the first five in that stage. A first stage divided into seven blocks is 17311 plus 17315 with two units. Count blocks, not slides.
How is a two-day Mohs surgery billed?
Bill the first layer performed on each day with the primary code, 17311 or 17313, and bill any further layers that same day with the add-on code. The primary code resets on day two, because claim edits reject an add-on stage that appears without its primary code on the same date of service.
How much does Medicare pay for 17311 in 2026?
The 2026 national office (non-facility) Medicare allowed amount for 17311 is about $667.02, using the non-QP conversion factor. The trunk and extremity first stage, 17313, is about $626.27. Actual payment varies by locality and payer.
Do you use modifier 59 or 51 with Mohs?
Use 59, or the more specific X-modifier where a payer requires it, on a first-stage line to flag a separate lesion treated the same day. Use 51 on the repair, since the closure is the lower-valued procedure in a combined Mohs-plus-repair session. Do not use 59 to try to unbundle pathology.
