2027 ICD-10-CM Diagnosis Code B03Smallpox

ICD-10-CM Codes›A00–B99›B00-B09›B03

ICD-10-CM B03
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

B03 is a billable ICD-10-CM diagnosis code for smallpox. 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 13 closely related codes. Coders also document this condition as alastrim. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Viral infection.

Code Identity

ICD-10-CM Code
B03
Billable Status
Yes — Valid for Submission
Code Describes
Smallpox
Short Description
Smallpox
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
CategoryB03Smallpox
This CodeB03Smallpox

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Alastrim
  • Flat-type smallpox
  • Hemorrhagic smallpox
  • Modified smallpox
  • Smallpox
  • Smallpox without rash
  • Variola major

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to B03: 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

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.-)

Notes

General instructions on how these codes are used.

  • In 1980 the 33rd World Health Assembly declared that smallpox had been eradicated.
  • The classification is maintained for surveillance purposes.

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

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

  • Smallpox

    an acute, highly contagious, often fatal infectious disease caused by an orthopoxvirus characterized by a biphasic febrile course and distinctive progressive skin eruptions. vaccination has succeeded in eradicating smallpox worldwide. (dorland, 28th ed)

Patient EducationClinical

Smallpox

Smallpox is a disease caused by the Variola major virus. Some experts say that over the centuries it has killed more people than all other infectious diseases combined. Worldwide vaccination stopped the spread of smallpox three decades ago. The last case was reported in 1977. Two research labs still keep small amounts of the virus.

Read the full article at MedlinePlus

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

Convert B03 to ICD-9-CMHistory

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

ICD-9-CM
050.0 Variola major
Approximate The match is approximate rather than exact.
ICD-9-CM
050.1 Alastrim
Approximate The match is approximate rather than exact.
ICD-9-CM
050.9 Smallpox NOS
Approximate The match is approximate rather than exact.

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 B03Overview

What is the ICD-10 code for smallpox?

The ICD-10-CM code for smallpox is B03. It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is B03 (Smallpox) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report smallpox on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

What MS-DRG does B03 group to?

When smallpox 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 B03 a CC or MCC?

CMS lists B03 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 13 closely related codes in its exclusion list.

What is the ICD-9 equivalent of B03?

Under the General Equivalence Mappings, smallpox converts to ICD-9-CM 050.0 (variola major), 050.1 (alastrim), and 050.9 (smallpox NOS). The mapping is approximate, so confirm the match fits the documentation.