2027 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 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

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 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 371 through 373. As a secondary diagnosis, it counts as a complication or comorbidity (CC) and moves an inpatient stay to a higher severity level within its MS-DRG family. It does not count, however, when the principal diagnosis is one of 24 closely related codes. 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

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to K35.209: its own notes plus those printed at Chapter 11. A note printed at a category, block or chapter applies to every code under it.

Applicable To

Conditions this code is used for: synonyms of the title or, for "other specified" codes, the conditions assigned to it. The list is not exhaustive.

  • (Acute) appendicitis with generalized peritonitis NOS

Excludes2

Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.

From Chapter 11 (K00-K95) Diseases of the digestive system applies to 863 codes
  • certain conditions originating in the perinatal period (P04-P96)
  • certain infectious and parasitic diseases (A00-B99)
  • complications of pregnancy, childbirth and the puerperium (O00-O9A)
  • congenital malformations, deformations and chromosomal abnormalities (Q00-Q99)
  • endocrine, nutritional and metabolic diseases (E00-E88)
  • injury, poisoning and certain other consequences of external causes (S00-T88)
  • neoplasms (C00-D49)
  • symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R94)

Source: CMS ICD-10-CM Tabular List. How to read instructional notes.

Referenced in Other NotesGuidance

Instructional notes printed at other codes that name K35.209, its category, or a range that includes it.

Excludes1 3

These codes carry an Excludes1 note naming K35.209: they are not reported together with it, unless the two conditions are unrelated.

  • K37 Unspecified appendicitis
    unspecified appendicitis with peritonitis (K35.2-, K35.3-) names K35.2-, which includes this code
  • K65 Peritonitis
    acute appendicitis with generalized peritonitis (K35.2-) names K35.2-, which includes this code
  • K65 Peritonitis
    peritonitis with or following appendicitis (K35.-) names K35.-, which includes this code

Excludes2 1

These codes carry an Excludes2 note naming K35.209: its condition is not part of those codes, and both may be reported when the patient has both.

  • K63.1 Perforation of intestine (nontraumatic)
    perforation (nontraumatic) of appendix (K35.2-, K35.3-) names K35.2-, which includes this code

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

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

Clinical InformationClinical

  • Appendicitis

    acute inflammation of the vermiform appendix.

Patient EducationClinical

Appendicitis

The appendix is a small, tube-like organ attached to the first part of the large intestine. It is located in the lower right part of the abdomen. It has no known function. A blockage inside of the appendix causes appendicitis. The blockage leads to increased pressure, problems with blood flow, and inflammation.

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

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 2025–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

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, 2026 through September 30, 2027.

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 372, 371, 373, with relative weights from 0.6945 to 1.7087 depending on complications. Higher weights mean higher Medicare reimbursement.

Is K35.209 a CC or MCC?

CMS lists K35.209 as a CC (complication or comorbidity) for FY 2027. Reported as a secondary diagnosis, it moves the inpatient stay to a higher-weighted DRG within its severity family. It does not count when the principal diagnosis is one of the 24 closely related codes in its exclusion list.