ICD-10 Code C84.00 – Mycosis fungoides, unspecified site (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code C84.00 – Mycosis fungoides, unspecified site
What it is
C84.00 identifies mycosis fungoides when the site is not specified. It is a cutaneous T-cell lymphoma that primarily affects the skin; use this code when the record does not document a more specific site.
Clinical signs
Clinical features vary; refer to documentation. Commonly noted findings include persistent patches, plaques, or tumors on the skin, sometimes with itching or scaling, but the exact stage and site should be confirmed.
When to use this code
Use C84.00 when the provider documents mycosis fungoides and does not name a specific anatomic site. It is appropriate for confirmed cases with nonspecific site documentation in the chart. If the note identifies a more precise site or subtype, code that instead.
Do not use for
Do not use this code for other cutaneous lymphomas or for skin lesions without a documented diagnosis of mycosis fungoides. Check documentation if the site is specified elsewhere in the record.
Coding tip
Look for the exact site and stage in the provider note before defaulting to C84.00.