ICD-10 Code K12.3 – Oral mucositis (ulcerative) (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code K12.3 – Oral mucositis (ulcerative)
What it is
K12.3 identifies ulcerative inflammation of the oral mucosa. It refers to painful sores or breakdown of the lining inside the mouth, often documented as oral mucositis with ulceration.
Clinical signs
Typical findings include visible oral ulcers, redness, swelling, and pain affecting the lips, cheeks, tongue, or gums. Clinical features vary; refer to documentation.
When to use this code
Use K12.3 when the record clearly documents ulcerative oral mucositis or equivalent wording, such as ulceration of the mouth lining. Code based on the provider’s diagnosis, not on nonspecific mouth pain alone. If the note does not specify ulceration, check documentation.
Do not use for
Do not use this code for non-ulcerative stomatitis, oral thrush, or simple aphthous ulcers unless the provider identifies ulcerative mucositis. Check documentation when the cause or site is unclear.
Coding tip
Assign K12.3 only when ulcerative mucositis is explicitly documented; otherwise, query or code the more specific recorded oral condition.