2026 ICD-10-CM Diagnosis Code A51.9Early syphilis, unspecified

ICD-10-CM Codes›A00–B99›A50-A64›A51

ICD-10-CM A51.9
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

A51.9 is a billable ICD-10-CM diagnosis code for early syphilis, unspecified. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 867 through 869. Coders also document this condition as early symptomatic syphilis. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Sexually transmitted infections (excluding HIV and hepatitis).

Code Identity

ICD-10-CM Code
A51.9
Billable Status
Yes — Valid for Submission
Code Describes
Early syphilis, unspecified
Short Description
Early syphilis, unspecified
Same as the full description in the CMS dataset.
Parent Code
A51
Early syphilis

Code Classification

ChapterA00–B99Certain infectious and parasitic diseases
SectionA50-A64Infections with a predominantly sexual mode of transmission
CategoryA51Early syphilis
This CodeA51.9Early syphilis, unspecified

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Early symptomatic syphilis

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Syphilis, syphilitic(acquired)
      • age under 2 years NOS
        • acquired
    • Syphilis, syphilitic(acquired)
      • early
    • Syphilis, syphilitic(acquired)
      • early
        • relapse (treated, untreated)
    • Syphilis, syphilitic(acquired)
      • early
        • symptomatic
    • Syphilis, syphilitic(acquired)
      • recently acquired, symptomatic

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR INF010
Sexually transmitted infections (excluding HIV and hepatitis)
Default principal diagnosis: inpatient Yes · outpatient Yes

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.

Convert A51.9 to ICD-9-CMHistory

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

ICD-9-CM
092.9 Early syphil latent 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 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About A51.9Overview

Is A51.9 (Early syphilis) a billable code?

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

What MS-DRG does A51.9 group to?

When early syphilis, unspecified is the principal diagnosis on an inpatient stay, it groups to MS-DRG 867, 868, 869, with relative weights from 0.7297 to 2.0932 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of A51.9?

Under the General Equivalence Mappings, early syphilis, unspecified converts to ICD-9-CM 092.9 (early syphil latent NOS). The mapping is approximate, so confirm the match fits the documentation.

Footnotes

[1] Not chronic - A diagnosis code that does not fit the criteria for chronic condition (duration, ongoing medical treatment, and limitations) is considered not chronic. Some codes designated as not chronic are acute conditions. Other diagnosis codes that indicate a possible chronic condition, but for which the duration of the illness is not specified in the code description (i.e., we do not know the condition has lasted 12 months or longer) also are considered not chronic.