ICD-10 Code K59.3 – Megacolon, not elsewhere classified (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code K59.3 – Megacolon, not elsewhere classified
What it is
K59.3 identifies megacolon that is not classified elsewhere. It refers to abnormal colonic dilation documented as a distinct diagnosis, rather than a symptom or a condition already coded in another category.
Clinical signs
Clinical features vary; refer to documentation. Commonly recorded findings include marked abdominal distention, constipation, reduced bowel function, or radiographic evidence of an enlarged colon.
When to use this code
Use K59.3 when the provider documents megacolon and does not link it to another more specific cause or codeable disorder. It also fits when the record clearly states megacolon, not elsewhere classified, without additional qualifying detail. Check documentation if the enlargement is secondary to another disease.
Do not use for
Do not use this code for constipation alone, ileus, or bowel obstruction unless the provider specifically documents megacolon. Also avoid it when another diagnosis better explains the colonic dilation.
Coding tip
Verify whether megacolon is primary or secondary, and code the more specific documented condition when available.