2026 ICD-10-CM Diagnosis Code B04Monkeypox

ICD-10-CM Codes›A00–B99›B00-B09›B04

ICD-10-CM B04
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

B04 is a billable ICD-10-CM diagnosis code for monkeypox. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 865 through 866. 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 15 closely related codes. Coders also document this condition as corneal disorder caused by monkeypox virus. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Viral infection.

Code Identity

ICD-10-CM Code
B04
Billable Status
Yes — Valid for Submission
Code Describes
Monkeypox
Short Description
Monkeypox
Same as the full description in the CMS dataset.
Chapter
B00-B09
Viral infections characterized by skin and mucous membrane lesions

Code Classification

ChapterA00–B99Certain infectious and parasitic diseases
SectionB00-B09Viral infections characterized by skin and mucous membrane lesions
CategoryB04Monkeypox
This CodeB04Monkeypox

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Corneal disorder caused by monkeypox virus
  • Encephalopathy caused by monkeypox virus
  • Mpox
  • Sepsis caused by monkeypox virus

Tabular List NotesGuidance

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

Inclusion Terms

  • Mpox

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 INF008
Viral infection
Default principal diagnosis: inpatient Yes · outpatient Yes

Patient EducationClinical

Mpox

Mpox, which used to be called monkeypox, is a disease caused by the monkeypox virus. This virus is in the same family of viruses as the smallpox virus.

The full article covers:

  • What is mpox?
  • What are the types of monkeypox viruses?
  • How does mpox spread?
  • What are the symptoms of mpox?
  • How is mpox diagnosed?
  • What are the treatments for mpox?
  • Can mpox be prevented?

Read the full article at MedlinePlus

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

Convert B04 to ICD-9-CMHistory

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

ICD-9-CM
059.01 Monkeypox
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 B04Overview

What is the ICD-10 code for monkeypox?

The ICD-10-CM code for monkeypox is B04. It is billable on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

Is B04 (Monkeypox) a billable code?

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

What MS-DRG does B04 group to?

When monkeypox is the principal diagnosis on an inpatient stay, it groups to MS-DRG 865, 866, with relative weights from 0.8696 to 1.4983 depending on complications. Higher weights mean higher Medicare reimbursement.

Is B04 a CC or MCC?

CMS lists B04 as a CC (complication or comorbidity) for FY 2026. 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 15 closely related codes in its exclusion list.

What is the ICD-9 equivalent of B04?

Under the General Equivalence Mappings, monkeypox converts to ICD-9-CM 059.01 (monkeypox). The mapping is a direct match.