ICD-10 Code K65.9 – Peritonitis, unspecified (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code K65.9 – Peritonitis, unspecified
What it is
K65.9 identifies peritonitis when the provider documents inflammation of the peritoneum but does not specify the cause, type, or site. Use it for a broad peritoneal infection or inflammation diagnosis when details are limited.
Clinical signs
Common findings include abdominal pain, tenderness, guarding, and signs of peritoneal irritation. Clinical features vary; refer to documentation for the documented cause, acuity, and any associated abdominal findings.
When to use this code
Use K65.9 when the record clearly states peritonitis but does not identify a more specific form, such as localized, generalized, or secondary peritonitis. It also fits when the provider documents peritonitis without further detail. If the cause is known, check documentation for a more specific code.
Do not use for
Do not use this code when the chart specifies a different peritonitis type, a postoperative complication, or another abdominal inflammatory condition. Check documentation before assigning K65.9.
Coding tip
Query for the cause and type of peritonitis whenever the note is vague, because a more specific code may be available.