ICD-10-CM 2027 diagnosis code
R51.9Headache, unspecified
R51.9 is a valid, billable ICD-10-CM code for headache, unspecified. It can be reported on claims for dates of service from October 1, 2026 – September 30, 2027.
Source: official FY2027 ICD-10-CM release from CDC/NCHS and CMS, effective October 1, 2026. Updated September 29, 2026. About our data
About R51.9
R51.9 is the ICD-10-CM diagnosis code for headache, unspecified. It belongs to category R51 (headache), block R50-R69 (general symptoms and signs) and chapter 18 (symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified). It is billable, so it can be reported on its own for dates of service from October 1, 2026 through September 30, 2027.
Within R51, choose R51.9 (unspecified) only when documentation doesn't support a more specific option: with orthostatic component, not elsewhere classified (R51.0).
It is not a CC or MCC, so as a secondary diagnosis it doesn't change the MS-DRG severity level.
In MS-DRG v44.0, it is part of the grouping logic for DRG 102 (Headaches with MCC, relative weight 1.1201) and DRG 103 (Headaches without MCC, relative weight 0.822), in MDC 01 (Diseases and Disorders of the Nervous System), as a principal or secondary diagnosis. The DRG a claim lands in depends on the principal diagnosis, procedures and any CC/MCC secondary diagnoses.
It was added in FY2021, effective October 1, 2020.
Coding notes
- Facial pain NOS
Notes that apply from higher levels
Instructions written at a parent level also apply to R51.9.
› From R51 Headache
Broader instructions also apply from Chapter 18: Symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified.
Alphabetic index entries
5 entriesTerms in the official ICD-10-CM index that lead to R51.9.
Codes whose notes reference R51.9
MS-DRG v44.0 grouping
All DRGs →Inpatient MS-DRGs this diagnosis can group to, as the principal or a secondary diagnosis, depending on the rest of the claim.
MDC 01 · Diseases and Disorders of the Nervous System
Code history
- 2016
- 2017
- 2018
- 2019
- 2020
- 2021
- 2022
- 2023
- 2024
- 2025
- 2026
- 2027
- FY2021 (effective 10/1/2020): Added
- No changes since FY2021.
Common questions about R51.9
Is R51.9 billable?
- Yes. R51.9 is a billable/specific ICD-10-CM code valid for FY2027 (October 1, 2026 – September 30, 2027).
Can R51.9 be used as a principal diagnosis?
- Yes. The Medicare Code Editor doesn't restrict R51.9 as a principal diagnosis.
Is R51.9 a CC or MCC?
- No. R51.9 is neither a CC nor an MCC under MS-DRG v44.0.
What DRG does R51.9 group to?
- R51.9 is used in the MS-DRG v44.0 logic for MS-DRG 102 (Headaches with MCC) and MS-DRG 103 (Headaches without MCC). Which one applies depends on whether it is the principal diagnosis and on the rest of the claim.