ICD-10-CM 2027 diagnosis code
G21.0Malignant neuroleptic syndrome
G21.0 is a valid, billable ICD-10-CM code for malignant neuroleptic syndrome. It can be reported on claims for dates of service from October 1, 2026 – September 30, 2027.
Code unchanged since ICD-10-CM took effect on October 1, 2015. Source: official FY2027 ICD-10-CM release from CDC/NCHS and CMS. Page updated September 29, 2026. About our data
About G21.0
G21.0 is the ICD-10-CM diagnosis code for malignant neuroleptic syndrome. It belongs to category G21 (secondary parkinsonism), block G20-G26 (extrapyramidal and movement disorders) and chapter 6 (diseases of the nervous system). It is billable, so it can be reported on its own for dates of service from October 1, 2026 through September 30, 2027.
Within G21 (secondary parkinsonism), G21.0 is specifically for malignant neuroleptic syndrome. Related codes cover other drug-induced secondary parkinsonism (G21.1), due to other external agents (G21.2), Postencephalitic parkinsonism (G21.3), vascular parkinsonism (G21.4), other secondary parkinsonism (G21.8) and unspecified (G21.9).
Don't report G21.0 together with the conditions in its Excludes1 note: neuroleptic induced parkinsonism (G21.11).
Use an additional code for adverse effect, if applicable, to identify drug (T43.3X5, T43.4X5, T43.505, T43.595).
As a secondary diagnosis it is an MCC (major complication or comorbidity), which can move an inpatient stay into the highest-paying "with MCC" MS-DRG of its family, unless the principal diagnosis excludes it.
In MS-DRG v44.0, it is part of the grouping logic for DRG 091 (Other Disorders of Nervous System with MCC, relative weight 1.7046), DRG 092 (Other Disorders of Nervous System with CC, relative weight 1.0239) and DRG 093 (Other Disorders of Nervous System without CC/MCC, relative weight 0.7783), 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 has been part of ICD-10-CM since the code set took effect on October 1, 2015 and hasn't changed since.
Before ICD-10, this condition was coded in ICD-9-CM as 333.92 (neuroleptic malignant syndrome).
Coding notes
Notes that apply from higher levels
Instructions written at a parent level also apply to G21.0.
› From G21 Secondary parkinsonism
Broader instructions also apply from Chapter 6: Diseases of the nervous system.
Alphabetic index entries
1 entriesTerms in the official ICD-10-CM index that lead to G21.0.
Codes whose notes reference G21.0
- G21.11Excludes1
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
ICD-9-CM equivalent
Converter →- 333.92Neuroleptic malignant syndromeexact
From the CMS 2018 General Equivalence Mappings (GEMs), the final GEMs release.
Code history
- 2016
- 2017
- 2018
- 2019
- 2020
- 2021
- 2022
- 2023
- 2024
- 2025
- 2026
- 2027
- FY2016 (effective 10/1/2015): Added (first year of ICD-10-CM)
- No changes since FY2016.
Common questions about G21.0
Is G21.0 billable?
- Yes. G21.0 is a billable/specific ICD-10-CM code valid for FY2027 (October 1, 2026 – September 30, 2027).
Can G21.0 be used as a principal diagnosis?
- Yes. The Medicare Code Editor doesn't restrict G21.0 as a principal diagnosis.
Is G21.0 a CC or MCC?
- G21.0 is an MCC (major complication or comorbidity) under MS-DRG v44.0, unless excluded by the principal diagnosis.
What DRG does G21.0 group to?
- G21.0 is used in the MS-DRG v44.0 logic for MS-DRG 091 (Other Disorders of Nervous System with MCC), MS-DRG 092 (Other Disorders of Nervous System with CC) and MS-DRG 093 (Other Disorders of Nervous System without CC/MCC). Which one applies depends on whether it is the principal diagnosis and on the rest of the claim.
What is the ICD-9 code for G21.0?
- The CMS General Equivalence Mappings map G21.0 to ICD-9-CM 333.92.