BackgroundThe information relating to the outcome specifically for juvenile dogs with meningoencephalitis of unknown etiology (MUE) is lacking.ObjectivesTo describe the clinical presentation, diagnostic findings, treatment, and outcome in a cohort of dogs with MUE <52 weeks old.AnimalsThirty‐four client‐owned dogs.MethodsMulticenter retrospective case series. Records from 5 referral centers were searched. Data was extracted from the medical records and referring veterinarians were contacted for survival data if this was not available from the record.ResultsThe mean age was 31 weeks; the youngest dog was 11 weeks and 3 dogs were <16 weeks old. Altered mentation (71%), ataxia (44%), seizures (29%), and circling (26%) were the most common presenting complaints. Neuroanatomical localization was to the forebrain (38%), multifocal (35%), brainstem (18%), and cerebellum (12%). Corticosteroid monotherapy (n = 15) and corticosteroid plus cytosine arabinoside (n = 15) were used in equal proportions. Outcome data was available for 26 dogs, 8 (31%) were alive at the time of data collection with a follow‐up range of 135 to 2944 days. Death or euthanasia was related to MUE in 17/18 dogs that died during the study period. Kaplan‐Meier survival analysis demonstrated a median survival time for all‐cause death of 84 days.ConclusionThe prognosis for MUE in this subset of dogs was considered poor.