2026 ICD-10-CM Diagnosis Code K35.209Acute appendicitis with generalized peritonitis, without abscess, unspecified as to perforation

ICD-10-CM Codes›K00–K95›K35-K38›K35

ICD-10-CM K35.209
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

K35.209 is a billable ICD-10-CM diagnosis code for acute appendicitis with generalized peritonitis, without abscess, unspecified as to perforation. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 371 through 373. Coders also document this condition as acute appendicitis with generalized peritonitis. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Appendicitis and other appendiceal conditions and Peritonitis and intra-abdominal abscess.

Code Identity

ICD-10-CM Code
K35.209
Billable Status
Yes — Valid for Submission
Code Describes
Acute appendicitis with generalized peritonitis, without abscess, unspecified as to perforation
Short Description
Ac appendicitis w gen peritonitis,w/o abscs,unsp as to perf
Parent Code
K35.20
Acute appendicitis with generalized peritonitis, without abscess

Code Classification

ChapterK00–K95Diseases of the digestive system
SectionK35-K38Diseases of appendix
CategoryK35Acute appendicitis
This CodeK35.209Acute appendicitis with generalized peritonitis, without abscess, unspecified as to perforation

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Acute appendicitis with generalized peritonitis
  • Acute appendicitis with peritonitis
  • Acute generalized peritonitis

Tabular List NotesGuidance

Coding notes and annotation back-references applicable to this code.

Inclusion Terms

  • (Acute) appendicitis with generalized peritonitis NOS

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Appendicitis(pneumococcal) (retrocecal)
      • with
        • peritonitis NEC
          • generalized
    • Appendicitis(pneumococcal) (retrocecal)
      • acute (catarrhal) (fulminating) (obstructive) (retrocecal) (suppurative)
        • with
          • peritonitis NEC
            • generalized
    • Peritonitis(adhesive) (bacterial) (fibrinous) (hemorrhagic) (idiopathic) (localized) (perforative) (primary) (with adhesions) (with effusion)
      • with or following
        • appendicitis
          • generalized

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR DIG009
Appendicitis and other appendiceal conditions
Default principal diagnosis: inpatient Yes · outpatient Yes
CCSR DIG016
Peritonitis and intra-abdominal abscess
Default principal diagnosis: inpatient No · outpatient No

Code History & ChangesHistory

Replacement K35.209 replaces the following previously assigned code(s):

  • K35.20 - Acute appendicitis with gen peritonitis, without abscess
FY 2024AddedAdded to the ICD-10-CM code setEffective October 1, 2023.
FY 2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About K35.209Overview

Is K35.209 a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report acute appendicitis with generalized peritonitis, without abscess, unspecified as to perforation on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does K35.209 group to?

When acute appendicitis with generalized peritonitis, without abscess, unspecified as to perforation is the principal diagnosis on an inpatient stay, it groups to MS-DRG 371, 372, 373, with relative weights from 0.7274 to 1.7731 depending on complications. Higher weights mean higher Medicare reimbursement.

Footnotes

[1] Not chronic - A diagnosis code that does not fit the criteria for chronic condition (duration, ongoing medical treatment, and limitations) is considered not chronic. Some codes designated as not chronic are acute conditions. Other diagnosis codes that indicate a possible chronic condition, but for which the duration of the illness is not specified in the code description (i.e., we do not know the condition has lasted 12 months or longer) also are considered not chronic.