ICD-10 Code B03 – Smallpox (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code B03 – Smallpox
What it is
B03 identifies smallpox, a severe viral infection caused by variola virus. It is used for confirmed cases of this eradicated disease, not for other poxvirus infections.
Clinical signs
Typical findings include fever, malaise, and a characteristic rash that progresses to deep, well-circumscribed lesions. Clinical features vary; refer to documentation.
When to use this code
Use B03 when the record clearly documents smallpox or variola infection. Code it for confirmed diagnosis, public health reporting, or historical records when the clinician specifies smallpox. Check documentation if the note only says “pox-like rash” or another orthopoxvirus.
Do not use for
Do not use B03 for chickenpox, mpox, or unspecified viral exanthems. If the documentation names another poxvirus or is unclear, select the more accurate code or check documentation.
Coding tip
Verify that the provider specifically documents smallpox; vague rash descriptions are not enough.