2026 ICD-10-CM Diagnosis Code A51Early syphilis

ICD-10-CM Codes›A00–B99›A50-A64›A51

ICD-10-CM A51
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

A51 is a non-billable ICD-10-CM category code for early syphilis, so it cannot be submitted on claims. Use a more specific code from this category instead, such as A51.0, A51.1, A51.2, and A51.31.

Code Identity

ICD-10-CM Code
A51
Billable Status
No — Non-Billable Category
Code Describes
Early syphilis
Chapter
A50-A64
Infections with a predominantly sexual mode of transmission

Code Classification

ChapterA00–B99Certain infectious and parasitic diseases
SectionA50-A64Infections with a predominantly sexual mode of transmission
CategoryA51Early syphilis
This CodeA51Early syphilis

Specific Coding for Early syphilisOverview

Non-specific codes like A51 require more characters. Use one of these billable codes instead:

  • Use A51.0 for Primary genital syphilis

  • Use A51.1 for Primary anal syphilis

  • Use A51.2 for Primary syphilis of other sites

  • A51.3 for Secondary syphilis of skin and mucous membranes

  • Use A51.31 for Condyloma latum

  • Use A51.32 for Syphilitic alopecia

  • Use A51.39 for Other secondary syphilis of skin

  • A51.4 for Other secondary syphilis

  • Use A51.41 for Secondary syphilitic meningitis

  • Use A51.42 for Secondary syphilitic female pelvic disease

  • Use A51.43 for Secondary syphilitic oculopathy

  • Use A51.44 for Secondary syphilitic nephritis

  • Use A51.45 for Secondary syphilitic hepatitis

  • Use A51.46 for Secondary syphilitic osteopathy

  • Use A51.49 for Other secondary syphilitic conditions

  • Use A51.5 for Early syphilis, latent

  • Use A51.9 for Early syphilis, unspecified

Patient EducationClinical

Syphilis

Syphilis is a sexually transmitted infection (STI) caused by bacteria. It infects the genital area, lips, mouth, or anus of both men and women. You usually get syphilis from sexual contact with someone who has it. It can also pass from mother to baby during pregnancy.

Read the full article at MedlinePlus

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

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 A51Overview

Is A51 (Early syphilis) a billable code?

No. This is a category header that groups the codes for early syphilis, and headers cannot be submitted on claims. Claims for early syphilis need a more specific code from this category, such as A51.0, A51.1, and A51.2.