Mohs Surgery CPT Coding: 17311 to 17315 and Stage Counting

The code structure

• 17311 — first stage, head, neck, hands, feet, genitalia, or any site with surgery directly involving muscle, cartilage, bone, tendon, major nerves or vessels. Up to five tissue blocks.
• 17312 — each additional stage at those sites, up to five blocks per stage.
• 17313 — first stage, trunk, arms or legs. Up to five tissue blocks.
• 17314 — each additional stage on the trunk, arms or legs.
• 17315 — each additional block beyond five within any single stage, reported per block.

What counts as a stage, and what counts as a block

A stage is one complete cycle: tissue removed, mapped, processed and read, with the result determining whether another cycle is needed. Removing more tissue after a positive margin begins a new stage. Two specimens taken in the same cycle from the same map do not create two stages — they create additional blocks within one stage.

The block count is the number of tissue blocks prepared and read within that stage. The first five are included in the stage code; the sixth and beyond are reported with 17315, once per block. Practices with complex head-and-neck cases routinely exceed five blocks and routinely fail to report the excess, and because the stage code still pays, nothing in the remittance flags the omission.

What the Mohs code already includes

The stage codes include the excision, the mapping, the frozen-section processing, the microscopic examination and the interpretation. Separate pathology codes for that same tissue are not reportable — the interpretation is what the Mohs code pays for. A separate diagnostic biopsy of a different lesion at the same session is reportable with the appropriate distinct-service modifier, but re-billing the Mohs tissue as surgical pathology is a duplicate claim.

Where a specimen from the Mohs site genuinely requires permanent sections or special stains beyond the frozen-section workflow, that is reportable, and the record needs to show why the additional work was required rather than routine.

Repairs after Mohs

Closure is not included in the Mohs codes. A simple, intermediate or complex repair, an adjacent tissue transfer, a flap or a graft is reported separately and coded by defect size and technique — with the defect measured after the final clear stage, not from the original lesion.

Repairs performed the same day as the Mohs stages need the appropriate modifier to release the bundling edit, and where the repair is performed by a different physician the reporting splits accordingly. Under-measuring the post-Mohs defect is common because the number recorded in the chart is often the lesion measured at consultation.