ICD-10 Code for Encephalitis
Also indexed as (chronic) (hemorrhagic) (idiopathic) (nonepidemic) (spurious) (subacute)
The ICD-10-CM code for encephalitis is G04.90 — Encephalitis and encephalomyelitis, unspecified. This is the code the Alphabetic Index gives for encephalitis with no further qualifier, valid for FY2027 (October 1, 2026 – September 30, 2027).
BillableUnspecified
G04.90 is billable but unspecified. If the documentation names a type, site or cause, one of the more specific codes below is likely expected.
Which encephalitis code should you use?
The Alphabetic Index lists 65 codes under Encephalitis. Which one applies depends on the qualifier documented in the record — the type, site, cause, or associated condition. Find the qualifier below, then verify the code in the Tabular List before using it.
By type
| acute | A86 | Unspecified viral encephalitis | |
| arboviral, arbovirus NEC | A85.2 | Arthropod-borne viral encephalitis, unspecified | |
| arthropod-borne NEC | A85.2 | Arthropod-borne viral encephalitis, unspecified | |
| Australian | A83.4 | Australian encephalitis | |
| California | A83.5 | California encephalitis | |
| Central European | A84.1 | Central European tick-borne encephalitis | |
| Czechoslovakian | A84.1 | Central European tick-borne encephalitis | |
| Dawson's | A81.1 | Subacute sclerosing panencephalitis | |
| diffuse sclerosing | A81.1 | Subacute sclerosing panencephalitis | |
| disseminated, acute | G04.00 | Acute disseminated encephalitis and encephalomyelitis, unspecified | |
| Eastern equine | A83.2 | Eastern equine encephalitis | |
| endemic | A86 | Unspecified viral encephalitis | |
| epidemic NEC | A86 | Unspecified viral encephalitis | |
| equine | A83.9 | Mosquito-borne viral encephalitis, unspecified | |
| Far Eastern | A84.0 | Far Eastern tick-borne encephalitis [Russian spring-summer encephalitis] | |
| following vaccination or other immunization procedure | G04.02 | Postimmunization acute disseminated encephalitis, myelitis and encephalomyelitis | |
| herpes zoster | B02.0 | Zoster encephalitis | |
| herpesviral | B00.4 | Herpesviral encephalitis | |
| Ilheus | A83.8 | Other mosquito-borne viral encephalitis | |
| inclusion body | A81.1 | Subacute sclerosing panencephalitis | |
| infectiousNEC | A86 | Unspecified viral encephalitis | |
| Japanese | A83.0 | Japanese encephalitis | |
| La Crosse | A83.5 | California encephalitis | |
| lethargica | A85.8 | Other specified viral encephalitis | |
| louping ill | A84.89 | Other tick-borne viral encephalitis | |
| lupus erythematosus, systemic | M32.19 | Other organ or system involvement in systemic lupus erythematosus | |
| lymphatica | A87.2 | Lymphocytic choriomeningitis | |
| Mengo | A85.8 | Other specified viral encephalitis | |
| meningococcal | A39.81 | Meningococcal encephalitis | |
| Murray Valley | A83.4 | Australian encephalitis | |
| otitic NEC | H66.40 | Suppurative otitis media, unspecified, unspecified ear | |
| parasitic NOS | B71.9 | Cestode infection, unspecified | |
| periaxial | G37.0 | Diffuse sclerosis of central nervous system | |
| periaxialis | G37.5 | Concentric sclerosis [Balo] of central nervous system | |
| postchickenpox | B01.11 | Varicella encephalitis and encephalomyelitis | |
| postexanthematous NEC | B09 | Unspecified viral infection characterized by skin and mucous membrane lesions | |
| postimmunization | G04.02 | Postimmunization acute disseminated encephalitis, myelitis and encephalomyelitis | |
| postinfectious NEC | G04.01 | Postinfectious acute disseminated encephalitis and encephalomyelitis (postinfectious ADEM) | |
| postmeasles | B05.0 | Measles complicated by encephalitis | |
| postvaccinal | G04.02 | Postimmunization acute disseminated encephalitis, myelitis and encephalomyelitis | |
| postvaricella | B01.11 | Varicella encephalitis and encephalomyelitis | |
| postviral NEC | A86 | Unspecified viral encephalitis | |
| Powassan | A84.81 | Powassan virus disease | |
| Rasmussen | G04.81 | Other encephalitis and encephalomyelitis | |
| Rio Bravo | A85.8 | Other specified viral encephalitis | |
| specified NEC | G04.81 | Other encephalitis and encephalomyelitis | |
| St. Louis | A83.3 | St Louis encephalitis | |
| subacute sclerosing | A81.1 | Subacute sclerosing panencephalitis | |
| summer | A83.0 | Japanese encephalitis | |
| suppurative | G04.81 | Other encephalitis and encephalomyelitis | |
| tick-borne | A84.9 | Tick-borne viral encephalitis, unspecified | |
| Torula, torular | B45.1 | Cerebral cryptococcosis | |
| toxic NEC | G92.8 | Other toxic encephalopathy | |
| trichinosis | B75 | Trichinellosis | |
| van Bogaert's | A81.1 | Subacute sclerosing panencephalitis | |
| Venezuelan equine | A92.2 | Venezuelan equine fever | |
| Vienna | A85.8 | Other specified viral encephalitis | |
| viral, virus | A86 | Unspecified viral encephalitis | |
| Western equine | A83.1 | Western equine encephalitis |
Encephalitis acute
| disseminated | G04.00 | Acute disseminated encephalitis and encephalomyelitis, unspecified | |
| inclusion body | A85.8 | Other specified viral encephalitis | |
| necrotizing hemorrhagic | G04.30 | Acute necrotizing hemorrhagic encephalopathy, unspecified | |
| disseminated › infectious | G04.01 | Postinfectious acute disseminated encephalitis and encephalomyelitis (postinfectious ADEM) | |
| disseminated › noninfectious | G04.81 | Other encephalitis and encephalomyelitis | |
| disseminated › postimmunization | G04.02 | Postimmunization acute disseminated encephalitis, myelitis and encephalomyelitis | |
| disseminated › postinfectious | G04.01 | Postinfectious acute disseminated encephalitis and encephalomyelitis (postinfectious ADEM) | |
| necrotizing hemorrhagic › postimmunization | G04.32 | Postimmunization acute necrotizing hemorrhagic encephalopathy | |
| necrotizing hemorrhagic › postinfectious | G04.31 | Postinfectious acute necrotizing hemorrhagic encephalopathy | |
| necrotizing hemorrhagic › specified NEC | G04.39 | Other acute necrotizing hemorrhagic encephalopathy |
Encephalitis due to
Encephalitis equine
Encephalitis herpesviral
Encephalitis in
| actinomycosis | A42.82 | Actinomycotic encephalitis | |
| adenovirus | A85.1 | Adenoviral encephalitis | |
| African trypanosomiasis | B56.9 | African trypanosomiasis, unspecified | |
| Chagas' disease | B57.42 | Meningoencephalitis in Chagas' disease | |
| cytomegalovirus | B25.8 | Other cytomegaloviral diseases | |
| enterovirus | A85.0 | Enteroviral encephalitis | |
| herpesvirus | B00.4 | Herpesviral encephalitis | |
| infectious disease NEC | B99 | Other and unspecified infectious diseases | not billable |
| listeriosis | A32.12 | Listerial meningoencephalitis | |
| measles | B05.0 | Measles complicated by encephalitis | |
| mumps | B26.2 | Mumps encephalitis | |
| naegleriasis | B60.2 | Naegleriasis | |
| parasitic disease NEC | B89 | Unspecified parasitic disease | |
| poliovirus | A80.9 | Acute poliomyelitis, unspecified | |
| rubella | B06.01 | Rubella encephalitis | |
| systemic lupus erythematosus | M32.19 | Other organ or system involvement in systemic lupus erythematosus | |
| toxoplasmosis | B58.2 | Toxoplasma meningoencephalitis | |
| tuberculosis | A17.82 | Tuberculous meningoencephalitis | |
| zoster | B02.0 | Zoster encephalitis | |
| herpesvirus › due to herpesvirus 6 | B10.01 | Human herpesvirus 6 encephalitis | |
| herpesvirus › due to herpesvirus 7 | B10.09 | Other human herpesvirus encephalitis | |
| herpesvirus › specified NEC | B10.09 | Other human herpesvirus encephalitis | |
| syphilis › congenital | A50.42 | Late congenital syphilitic encephalitis | |
| syphilis › late | A52.14 | Late syphilitic encephalitis | |
| toxoplasmosis › congenital | P37.1 | Congenital toxoplasmosis |
Encephalitis Russian
Encephalitis viral, virus
| arthropod-borne NEC | A85.2 | Arthropod-borne viral encephalitis, unspecified | |
| specified type NEC | A85.8 | Other specified viral encephalitis | |
| tick-borne, specified NEC | A84.89 | Other tick-borne viral encephalitis | |
| arthropod-borne NEC › mosquito-borne | A83.9 | Mosquito-borne viral encephalitis, unspecified | |
| arthropod-borne NEC › tick-borne | A84.9 | Tick-borne viral encephalitis, unspecified | |
| arthropod-borne NEC › mosquito-borne › Australian X disease | A83.4 | Australian encephalitis | |
| arthropod-borne NEC › mosquito-borne › California virus | A83.5 | California encephalitis | |
| arthropod-borne NEC › mosquito-borne › Eastern equine | A83.2 | Eastern equine encephalitis | |
| arthropod-borne NEC › mosquito-borne › Japanese | A83.0 | Japanese encephalitis | |
| arthropod-borne NEC › mosquito-borne › Murray Valley | A83.4 | Australian encephalitis | |
| arthropod-borne NEC › mosquito-borne › specified NEC | A83.8 | Other mosquito-borne viral encephalitis | |
| arthropod-borne NEC › mosquito-borne › St. Louis | A83.3 | St Louis encephalitis | |
| arthropod-borne NEC › mosquito-borne › type B | A83.0 | Japanese encephalitis |
Index terms and codes are reproduced from the official ICD-10-CM FY2027 release. The Alphabetic Index is a finding aid — a code must always be verified in the Tabular List before it is reported. Data sources