ICD-10-CM 2027
ICD-10 code for mononucleosis
From the official ICD-10-CM alphabetic index entry “Mononucleosis, infectious”. Page updated September 29, 2026.
About coding mononucleosis
The ICD-10-CM code for mononucleosis is B27.90 (Infectious mononucleosis, unspecified without complication). The official index lists 19 more specific codes, so check the documentation for details such as type, cause, site or severity before settling on B27.90.
Within B27.9, choose B27.90 (without complication) only when documentation doesn't support a more specific option: with polyneuropathy (B27.91), with meningitis (B27.92) and with other complication (B27.99).
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 865 (Viral Illness with MCC, relative weight 1.3485) and DRG 866 (Viral Illness without MCC, relative weight 0.8692), in MDC 18 (Infectious and Parasitic Diseases, Systemic or Unspecified Sites), as a principal or secondary diagnosis. The DRG a claim lands in depends on the principal diagnosis, procedures and any CC/MCC secondary diagnoses.
More specific mononucleosis codes (official index)
- with
- complication NEC B27.99 — Infectious mononucleosis, unspecified with other complication
- meningitis B27.92 — Infectious mononucleosis, unspecified with meningitis
- polyneuropathy B27.91 — Infectious mononucleosis, unspecified with polyneuropathy
- cytomegaloviral B27.10 — Cytomegaloviral mononucleosis without complications
- with
- complication NEC B27.19 — Cytomegaloviral mononucleosis with other complication
- meningitis B27.12 — Cytomegaloviral mononucleosis with meningitis
- polyneuropathy B27.11 — Cytomegaloviral mononucleosis with polyneuropathy
- Epstein-Barr (virus) B27.00 — Gammaherpesviral mononucleosis without complication
- with
- complication NEC B27.09 — Gammaherpesviral mononucleosis with other complications
- meningitis B27.02 — Gammaherpesviral mononucleosis with meningitis
- polyneuropathy B27.01 — Gammaherpesviral mononucleosis with polyneuropathy
- gammaherpesviral B27.00 — Gammaherpesviral mononucleosis without complication
- with
- complication NEC B27.09 — Gammaherpesviral mononucleosis with other complications
- meningitis B27.02 — Gammaherpesviral mononucleosis with meningitis
- polyneuropathy B27.01 — Gammaherpesviral mononucleosis with polyneuropathy
- specified NEC B27.80 — Other infectious mononucleosis without complication
- with
- complication NEC B27.89 — Other infectious mononucleosis with other complication
- meningitis B27.82 — Other infectious mononucleosis with meningitis
- polyneuropathy B27.81 — Other infectious mononucleosis with polyneuropathy
Common questions about mononucleosis ICD-10 codes
What is the ICD-10 code for mononucleosis?
- B27.90 — Infectious mononucleosis, unspecified without complication. More specific codes apply when the documentation supports them: B27.99, B27.92, B27.91, B27.10 and others below.
What is the ICD-10 code for cytomegaloviral mononucleosis?
- B27.10 — Cytomegaloviral mononucleosis without complications.
What is the ICD-10 code for epstein-barr mononucleosis?
- B27.00 — Gammaherpesviral mononucleosis without complication.
What is the ICD-10 code for gammaherpesviral mononucleosis?
- B27.00 — Gammaherpesviral mononucleosis without complication.
Is B27.90 billable?
- Yes. B27.90 is a billable/specific ICD-10-CM code valid for FY2027 (October 1, 2026 – September 30, 2027).
Can B27.90 be used as a principal diagnosis?
- Yes. The Medicare Code Editor doesn't restrict B27.90 as a principal diagnosis.
Is B27.90 a CC or MCC?
- No. B27.90 is neither a CC nor an MCC under MS-DRG v44.0.