2026 ICD-10-CM Diagnosis Code K66.9Disorder of peritoneum, unspecified

ICD-10-CM Codes›K00–K95›K65-K68›K66

ICD-10-CM K66.9
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

K66.9 is a billable ICD-10-CM diagnosis code for disorder of peritoneum, unspecified. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 393 through 395. Coders also document this condition as disorder of pelvic peritoneum. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Other specified and unspecified gastrointestinal disorders.

Code Identity

ICD-10-CM Code
K66.9
Billable Status
Yes — Valid for Submission
Code Describes
Disorder of peritoneum, unspecified
Short Description
Disorder of peritoneum, unspecified
Same as the full description in the CMS dataset.
Parent Code
K66
Other disorders of peritoneum

Code Classification

ChapterK00–K95Diseases of the digestive system
SectionK65-K68Diseases of peritoneum and retroperitoneum
CategoryK66Other disorders of peritoneum
This CodeK66.9Disorder of peritoneum, unspecified

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Disorder of pelvic peritoneum
  • Disorder of peritoneum

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.

    • Disease, diseased
      • peritoneum

Clinical ClassificationClinical

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

CCSR DIG025
Other specified and unspecified gastrointestinal disorders
Default principal diagnosis: inpatient Yes · outpatient Yes

Patient EducationClinical

Peritoneal Disorders

Your peritoneum is the tissue that lines your abdominal wall and covers most of the organs in your abdomen. A liquid, peritoneal fluid, lubricates the surface of this tissue.

Read the full article at MedlinePlus

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

Convert K66.9 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
568.9 Peritoneal disorder NOS
Exact Match The mapping is direct, with no qualifiers.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About K66.9Overview

Is K66.9 (Other disorders of peritoneum) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report disorder of peritoneum, unspecified on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does K66.9 group to?

When disorder of peritoneum, unspecified is the principal diagnosis on an inpatient stay, it groups to MS-DRG 393, 394, 395, with relative weights from 0.6490 to 1.5993 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of K66.9?

Under the General Equivalence Mappings, disorder of peritoneum, unspecified converts to ICD-9-CM 568.9 (peritoneal disorder NOS). The mapping is a direct match.

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.