ICD-10-CM 2027 diagnosis code

G91Hydrocephalus

Not billable — use a more specific code

G91 is a header code, so it can't be reported by itself. Choose one of the 7 more specific codes beneath it.

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 G91

G91 is the ICD-10-CM diagnosis code for hydrocephalus. It belongs to block G89-G99 (other disorders of the nervous system) and chapter 6 (diseases of the nervous system). It is a header code, so it can't be reported by itself; one of its 7 subcodes must be used instead.

To report this condition, pick the subcode that matches the documentation: G91.0 (hydrocephalus), G91.1 (hydrocephalus), G91.2 (hydrocephalus), G91.3 (unspecified), G91.4 (in diseases classified elsewhere), G91.8 (hydrocephalus) and G91.9 (unspecified).

Don't report G91 together with the conditions in its Excludes1 note: Arnold-Chiari syndrome with hydrocephalus (Q07.-), congenital hydrocephalus (Q03.-) and spina bifida with hydrocephalus (Q05.-).

It has been part of ICD-10-CM since the code set took effect on October 1, 2015 and hasn't changed since.

Specific codes under G91

Coding notes

IncludesFurther defines the content of the category

acquired hydrocephalus

Excludes1Not coded here — never report together with this code

Arnold-Chiari syndrome with hydrocephalus (Q07.-)
congenital hydrocephalus (Q03.-)
spina bifida with hydrocephalus (Q05.-)

Notes that apply from higher levels

Instructions written at a parent level also apply to G91.

Broader instructions also apply from Chapter 6: Diseases of the nervous system.

Codes whose notes reference G91

Q03Excludes1

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 G91

Is G91 billable?: No. G91 is a header code. Report one of its more specific subcodes instead.