2026 ICD-10-CM Diagnosis Code K59.31Toxic megacolon

ICD-10-CM Codes›K00–K95›K55-K64›K59

ICD-10-CM K59.31
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

K59.31 is a billable ICD-10-CM diagnosis code for toxic megacolon. 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 drug-induced megacolon. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Drug induced or toxic related condition and Other specified and unspecified gastrointestinal disorders.

Code Identity

ICD-10-CM Code
K59.31
Billable Status
Yes — Valid for Submission
Code Describes
Toxic megacolon
Short Description
Toxic megacolon
Same as the full description in the CMS dataset.
Parent Code
K59.3
Megacolon, not elsewhere classified

Code Classification

ChapterK00–K95Diseases of the digestive system
SectionK55-K64Other diseases of intestines
CategoryK59Other functional intestinal disorders
This CodeK59.31Toxic megacolon

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Drug-induced megacolon
  • Secondary acquired megacolon
  • Toxic megacolon due to ulcerative colitis
  • Toxic state
  • Toxic state due to colonic dilatation

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.

    • Dilatation
      • colon
        • toxic
    • Megacolon(acquired) (functional) (not Hirschsprung's disease) (in)
      • toxic NEC

Clinical ClassificationClinical

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

CCSR INJ030
Drug induced or toxic related condition
Default principal diagnosis: inpatient No · outpatient No
CCSR DIG025
Other specified and unspecified gastrointestinal disorders
Default principal diagnosis: inpatient Yes · outpatient Yes

Convert K59.31 to ICD-9-CMHistory

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

ICD-9-CM
556.9 Ulceratve colitis unspcf
Approximate The match is approximate rather than exact.

Code History & ChangesHistory

Replacement K59.31 replaces the following previously assigned code(s):

  • K59.3 - Megacolon, not elsewhere classified
FY 2018AddedAdded to the ICD-10-CM code setEffective October 1, 2017.
FY 2019–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About K59.31Overview

Is K59.31 (Megacolon, not elsewhere classified) a billable code?

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

What MS-DRG does K59.31 group to?

When toxic megacolon 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 K59.31?

Under the General Equivalence Mappings, toxic megacolon converts to ICD-9-CM 556.9 (ulceratve colitis unspcf). The mapping is approximate, so confirm the match fits the documentation.

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.