ICD-10-CM 2027 diagnosis code

B27Infectious mononucleosis

Not billable — use a more specific code

B27 is a header code, so it can't be reported by itself. Choose one of the 4 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 B27

B27 is the ICD-10-CM diagnosis code for infectious mononucleosis. It belongs to block B25-B34 (other viral diseases) and chapter 1 (certain infectious and parasitic diseases). It is a header code, so it can't be reported by itself; one of its 4 subcodes must be used instead.

To report this condition, pick the subcode that matches the documentation: B27.0 (mononucleosis), B27.1 (mononucleosis), B27.8 (mononucleosis) and B27.9 (unspecified).

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 B27

Coding notes

IncludesFurther defines the content of the category

glandular fever
monocytic angina
Pfeiffer's disease

Notes that apply from higher levels

Instructions written at a parent level also apply to B27.

Broader instructions also apply from Chapter 1: Certain infectious and parasitic diseases.

Codes whose notes reference B27

D72.821Excludes1
G02Excludes1
J02.8Excludes1

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 B27

Is B27 billable?: No. B27 is a header code. Report one of its more specific subcodes instead.