2027 ICD-10-CM Diagnosis Code B04Monkeypox

ICD-10-CM Codes›A00–B99›B00-B09›B04

ICD-10-CM B04
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

B04 is a billable ICD-10-CM diagnosis code for monkeypox. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) 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

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to B04: its own notes plus those printed at Chapter 1. A note printed at a category, block or chapter applies to every code under it.

Includes

Further defines, or gives examples of, the content of the category.

From Chapter 1 (A00-B99) Certain infectious and parasitic diseases applies to 1,068 codes
  • diseases generally recognized as communicable or transmissible

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.

  • Mpox

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 1 (A00-B99) Certain infectious and parasitic diseases applies to 1,068 codes
  • carrier or suspected carrier of infectious disease (Z22.-)
  • certain localized infections - see body system-related chapters
  • infectious and parasitic diseases complicating pregnancy, childbirth and the puerperium (O98.-)
  • infectious and parasitic diseases specific to the perinatal period (P35-P39)
  • influenza and other acute respiratory infections (J00-J22)

Use Additional Code

Add a second code, after this one, to fully describe the condition.

From Chapter 1 (A00-B99) Certain infectious and parasitic diseases applies to 1,068 codes
  • code to identify resistance to antimicrobial drugs (Z16.-)

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

Referenced in Other NotesGuidance

Instructional notes printed at other codes that name B04, its category, or a range that includes it.

Excludes2 1

These codes carry an Excludes2 note naming B04: its condition is not part of those codes, and both may be reported when the patient has both.

  • B08.0 Other orthopoxvirus infections
    monkeypox (B04)

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

Clinical InformationClinical

  • Mpox, Monkeypox

    a viral disease infecting primates and rodents. its clinical presentation in humans is similar to smallpox including fever; headache; cough; and a painful rash. it is caused by monkeypox virus and is usually transmitted to humans through bites or via contact with an animal's blood. interhuman transmission is relatively low (significantly less than smallpox).

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 2017–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

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, 2026 through September 30, 2027.

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, 2026 through September 30, 2027.

What MS-DRG does B04 group to?

When monkeypox is the principal diagnosis on an inpatient stay, it groups to MS-DRG 866, 865, with relative weights from 0.8691 to 1.3153 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 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 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.