2026 ICD-10-CM Diagnosis Code B27Infectious mononucleosis

ICD-10-CM Codes›A00–B99›B25-B34›B27

ICD-10-CM B27
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

B27 is a non-billable ICD-10-CM category code for infectious mononucleosis, so it cannot be submitted on claims. Use a more specific code from this category instead, such as B27.00, B27.01, B27.02, and B27.09.

Code Identity

ICD-10-CM Code
B27
Billable Status
No — Non-Billable Category
Code Describes
Infectious mononucleosis
Chapter
B25-B34
Other viral diseases

Code Classification

ChapterA00–B99Certain infectious and parasitic diseases
SectionB25-B34Other viral diseases
CategoryB27Infectious mononucleosis
This CodeB27Infectious mononucleosis

Specific Coding for Infectious mononucleosisOverview

Non-specific codes like B27 require more characters. Use one of these billable codes instead:

  • B27.0 for Gammaherpesviral mononucleosis

  • Use B27.00 for Gammaherpesviral mononucleosis without complication

  • Use B27.01 for Gammaherpesviral mononucleosis with polyneuropathy

  • Use B27.02 for Gammaherpesviral mononucleosis with meningitis

  • Use B27.09 for Gammaherpesviral mononucleosis with other complications

  • B27.1 for Cytomegaloviral mononucleosis

  • Use B27.10 for Cytomegaloviral mononucleosis without complications

  • Use B27.11 for Cytomegaloviral mononucleosis with polyneuropathy

  • Use B27.12 for Cytomegaloviral mononucleosis with meningitis

  • Use B27.19 for Cytomegaloviral mononucleosis with other complication

  • B27.8 for Other infectious mononucleosis

  • Use B27.80 for Other infectious mononucleosis without complication

  • Use B27.81 for Other infectious mononucleosis with polyneuropathy

  • Use B27.82 for Other infectious mononucleosis with meningitis

  • Use B27.89 for Other infectious mononucleosis with other complication

  • B27.9 for Infectious mononucleosis, unspecified

  • Use B27.90 for Infectious mononucleosis, unspecified without complication

  • Use B27.91 for Infectious mononucleosis, unspecified with polyneuropathy

  • Use B27.92 for Infectious mononucleosis, unspecified with meningitis

  • Use B27.99 for Infectious mononucleosis, unspecified with other complication

Tabular List NotesGuidance

Coding notes and annotation back-references applicable to this code.

Includes

  • glandular fever
  • monocytic angina
  • Pfeiffer's disease

Clinical InformationClinical

  • Fatigue Syndrome, Chronic

    a syndrome characterized by persistent or recurrent fatigue, diffuse musculoskeletal pain, sleep disturbances, and subjective cognitive impairment of 6 months duration or longer. symptoms are not caused by ongoing exertion; are not relieved by rest; and result in a substantial reduction of previous levels of occupational, educational, social, or personal activities. minor alterations of immune, neuroendocrine, and autonomic function may be associated with this syndrome. there is also considerable overlap between this condition and fibromyalgia. (from semin neurol 1998;18(2):237-42; ann intern med 1994 dec 15;121(12): 953-9)

  • Herpesvirus 4, Human

    the type species of lymphocryptovirus, subfamily gammaherpesvirinae, infecting b-cells in humans. it is thought to be the causative agent of infectious mononucleosis and is strongly associated with oral hairy leukoplakia (leukoplakia, hairy;), burkitt lymphoma; and other malignancies.

  • Infectious Mononucleosis

    a common, acute infection usually caused by the epstein-barr virus (herpesvirus 4, human). there is an increase in mononuclear white blood cells and other atypical lymphocytes, generalized lymphadenopathy, splenomegaly, and occasionally hepatomegaly with hepatitis.

  • Fibromyalgia

    a common nonarticular rheumatic syndrome characterized by myalgia and multiple points of focal muscle tenderness to palpation (trigger points). muscle pain is typically aggravated by inactivity or exposure to cold. this condition is often associated with general symptoms, such as sleep disturbances, fatigue, stiffness, headaches, and occasionally depression. there is significant overlap between fibromyalgia and the chronic fatigue syndrome (fatigue syndrome, chronic). fibromyalgia may arise as a primary or secondary disease process. it is most frequent in females aged 20 to 50 years. (from adams et al., principles of neurology, 6th ed, p1494-95)

Patient EducationClinical

Infectious Mononucleosis

Infectious mononucleosis (mono) is a disease caused by viruses.The most common cause is the Epstein-Barr virus (EBV). Mono is contagious, which means it can spread from person to person. It is common among teenagers and young adults, especially college students.

The full article covers:

  • What is infectious mononucleosis (mono)?
  • What causes infectious mononucleosis (mono)?
  • What are the symptoms of infectious mononucleosis (mono)?
  • How is infectious mononucleosis (mono) diagnosed?
  • What are the treatments for infectious mononucleosis (mono)?
  • Can infectious mononucleosis (mono) be prevented?

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About B27Overview

Is B27 (Infectious mononucleosis) a billable code?

No. This is a category header that groups the codes for infectious mononucleosis, and headers cannot be submitted on claims. Claims for infectious mononucleosis need a more specific code from this category, such as B27.00, B27.01, and B27.02.