Mohs micrographic surgery billing: 17311–17315 and split billing.
Mohs is the only dermatology code family that's staged, billed by tissue block count, and gated behind a single structural rule that decides whether the whole case is billable as Mohs at all — the same physician has to be both the surgeon and the pathologist, at every stage. This guide covers the full code family with a worked multi-stage example, exactly how billing splits when a second physician handles reconstruction or pathology, and the five active MAC-specific Mohs LCDs confirmed live against the CMS Coverage Database.
Key takeaways
- The dual-role rule is a compliance gate, not a documentation nicety. If a different physician reads the pathology, the case isn't billable as Mohs under any circumstances — it has to be coded as excision plus separate pathology instead.
- +17315 counts blocks per stage, not per case. A case can run five stages and never trigger it, or trigger multiple units in a single busy stage — the two counts aren't related.
- Reconstructive closure by a second physician is billed entirely separately under that physician's own NPI, with its own repair, flap, or graft code — no special modifier links the two claims.
- Five different MACs run five different Mohs LCDs — confirmed by document ID against the CMS Coverage Database — and "the LCD says" is not a citation any of them will accept.
The Mohs code family
Mohs billing runs on two axes: location (which determines the base first-stage and additional-stage codes) and tissue block count within each stage (which determines whether the add-on block code applies). Every code in the family requires the physician to personally map, section, and interpret the tissue — that's what separates Mohs from an excision with a separate pathology read, covered below.
| Code | What it reports | Location / scope |
|---|---|---|
17311 | First stage, up to 5 tissue blocks | Head, neck, hands, feet, genitalia |
+17312 | Each additional stage after the first, same session, up to 5 tissue blocks per stage (add-on) | Head, neck, hands, feet, genitalia |
17313 | First stage, up to 5 tissue blocks | Trunk, arms, legs |
+17314 | Each additional stage after the first, same session, up to 5 tissue blocks per stage (add-on) | Trunk, arms, legs |
+17315 | Each additional tissue block beyond the first 5, within any single stage (add-on; usable with 17311–17314) | Any location |
A case is billed by location once — the anatomic site doesn't change mid-case, so a single encounter reports either the 17311/+17312 pair or the 17313/+17314 pair, never both. +17315 is the code that trips up block-count math: it's counted per stage, not across the whole case, and it only starts once a single stage's block count passes five.
| Stage | Tissue blocks examined | Codes billed for this stage |
|---|---|---|
| Stage 1 | 4 blocks | 17311 ×1 (first stage, within the 5-block allowance) |
| Stage 2 | 7 blocks | +17312 ×1 (additional stage) plus +17315 ×2 (blocks 6 and 7, beyond the first 5) |
| Stage 3 | 3 blocks | +17312 ×1 (additional stage, no +17315 — under 5 blocks) |
Total claim for that case: one unit of 17311, two units of +17312, and two units of +17315. The tissue-block count for +17315 has to come from the physician's own operative and pathology log, block by block and stage by stage — not backed into from a total case block count, which would either miss units the stage genuinely earned or create units the documentation doesn't support.
The single-physician dual-role requirement
The rule that decides whether any code in this family applies at all: the same physician has to act as both the surgeon who removes the tissue and the pathologist who examines it under the microscope, for every single stage of the case. That dual role — the surgeon reading their own frozen sections in real time and deciding whether margins are clear before the patient leaves the chair — is the entire clinical and billing definition of Mohs surgery. It's not a preference or a best practice; it's what distinguishes the code family from a standard excision.
If a different physician interprets the pathology — a dermatopathologist reading slides sent out from a Mohs suite that doesn't have an on-site reader, for instance — the case cannot be coded as Mohs, full stop. Instead, code the surgical removal as a standard excision (11400–11446 for benign, 11600–11646 for malignant, selected by size and location the same way as any other excision) and code the pathologist's interpretation separately, under the pathologist's own NPI, using the appropriate frozen-section or surgical pathology code for the work actually performed. Billing 17311–17315 without the dual role documented and true is one of the more consequential errors in dermatology coding, because on audit it isn't a pricing dispute — it's a compliance finding.
- 1Documentation that supports the dual role. The operative and pathology log should show the same physician's name and NPI on both the surgical removal entry and the pathology interpretation entry, for every stage, ideally with a timestamp per stage.
- 2A covering pathologist reading slides, even occasionally, breaks the dual-role requirement for any stage that pathologist reads — not just for that stage's billing, but for how the whole case has to be evaluated on audit.
- 3Group practices with multiple Mohs surgeons can each independently meet the dual-role rule on their own cases; the requirement is per-case same-physician, not one physician for the whole practice.
Split billing: when reconstruction is a separate claim
The Mohs surgeon's own claim covers tumor removal and margin clearance only — 17311/17313 plus the add-ons above. Reconstructive closure of the resulting defect is a separate procedure, coded and billed independently of the Mohs codes, whether it's performed by the same physician immediately afterward or referred out to a different one.
- The Mohs surgeon bills 17311–17315 for the excision stages, plus the appropriate repair, flap, or graft code (12031–12057, 13100–13153, 14000–14302, 15002–15261, depending on defect and closure method) for the reconstruction, on the same claim.
- Simple, single-layer closure of the final Mohs defect follows the same bundling logic as any excision: it's included, not separately billed.
- The reconstructive surgeon (often plastics or facial plastics for complex head/neck defects) bills their own repair/flap/graft code under their own NPI, on their own claim — there is no special modifier that links the two claims together.
- Documentation on both sides should reference the same date of service and the same defect, so a payer reviewing either claim can see the case makes sense as a whole, but each physician's claim stands on its own coding logic.
The most common split-billing error isn't a coding mistake so much as a coordination gap: the Mohs surgeon's office bills the excision stages promptly, while the reconstructive surgeon's claim goes out separately (sometimes days later, if closure is scheduled for a follow-up visit) and uses a diagnosis code that doesn't match what the Mohs surgeon's claim used, which can read as inconsistent to a payer even when both codes are individually correct. Keep the diagnosis code consistent across both claims when the closure is billed the same date as the Mohs procedure.
MAC-specific Mohs LCD coverage
Mohs coverage is written and maintained per Medicare Administrative Contractor, not nationally — "the LCD says" is not a usable citation without naming which MAC. We confirmed five active local coverage documents directly against the CMS Coverage Database.
| Document | MAC | Effective date |
|---|---|---|
L34961 | Novitas Solutions | 11/14/2019 |
L33436 | Palmetto GBA | 11/16/2023 |
L33689 | First Coast Service Options | 01/08/2019 |
L35494 | WPS Insurance Corporation | 10/31/2024 |
L34195 | CGS Administrators | 05/07/2026 |
Noridian Healthcare Solutions also publishes its own active Mohs LCD (L35702, effective 10/23/2025), confirmed alongside the five above — find your practice's MAC first, then pull that specific document, not a generic search result. Effective dates alone tell you these documents don't move in lockstep: CGS revised its Mohs LCD as recently as May 2026, while First Coast's has stood since January 2019, which means the two MACs are very unlikely to be enforcing identical documentation and medical-necessity criteria right now even though both cover the same code family.
⚠️ The document IDs, contractor names, and effective dates above were confirmed live against the CMS Coverage Database. The full covered-diagnosis lists, tissue-block documentation requirements, and any staging or recurrence-risk criteria written inside each MAC's specific document were not independently re-verified in this build — the underlying Medicare Coverage Database article pages have returned access errors to automated retrieval in this environment, and this session's web search budget was also exhausted before that text could be cross-checked through a secondary source. Pull each MAC's document text directly, by the ID above, before finalizing a coverage rule, an order set, or an appeal argument against it — MAC-specific coverage articles are exactly where Mohs LCDs tend to diverge in practice, even when the underlying LCD titles look identical.
Before a Mohs claim goes out, reconcile the stage and block-count line items on the CMS-1500 against the operative and pathology log, line by line. Mismatched stage or block counts between the claim and the physician's own documentation are the single most common audit trigger in Mohs billing — more so than the dual-role rule itself, because it's the easiest thing for an auditor to check without any clinical judgment at all.
Not confident your Mohs claims are staged and coded correctly?
We'll audit a sample of your recent Mohs claims against your operative and pathology logs for stage-count, block-count, and dual-role documentation gaps.
Frequently asked questions
What's the difference between 17311/17313 and the add-on codes 17312/17314?
17311 and 17313 report the first stage of a Mohs case, split by location — 17311 for head, neck, hands, feet, or genitalia, and 17313 for trunk, arms, or legs — and each covers up to five tissue blocks examined in that stage. +17312 and +17314 are add-on codes for every additional stage beyond the first at the same site, one unit per additional stage, again up to five blocks each. A three-stage case on the scalp is coded as one unit of 17311 plus two units of +17312, not three units of anything.
When does the add-on code +17315 apply?
+17315 reports each additional tissue block beyond the first five examined within any single stage, regardless of which location code or which stage it occurs in. If stage two of a case produces seven tissue blocks, that stage is still one unit of +17312 (the stage itself), plus two units of +17315 for the two blocks beyond the first five. Blocks are counted per stage, not summed across the whole case, so a case with five stages of four blocks each never triggers +17315 at all even though the case-wide block count is high.
How do we bill Mohs surgery when the surgeon and pathologist are two different physicians?
It isn't billed as Mohs at all in that scenario, because the Mohs code family requires the same physician to both remove the tissue and examine it microscopically at every stage. When a second physician reads the slides, the case is coded as a standard excision (11400-11446 benign, 11600-11646 malignant, by size and location) for the surgical removal, plus a separate pathology code for the professional interpretation, billed under the pathologist's own NPI. Reconstructive closure performed by a different physician than the one who removed the tumor is billed the same way — under that physician's own NPI, using the appropriate repair, flap, or graft code for the closure actually performed, independent of how the excision itself was coded.
Verify before billing. CPT is a registered trademark of the American Medical Association; codes here are paraphrased, not reproduced from the CPT Professional edition. CPT, HCPCS and ICD-10 codes, coverage policy, and bundling edits change, including annual code-set updates. This page reflects standard industry practice and is provided for general education — it is not a substitute for your own compliance review, your current payer contracts, or the current-year code sets. Confirm requirements against your specific payer mix before submitting claims.