BACKGROUND: Cerebellar mutism in children occurs after posterior fossa tumor resection and can have lasting effects on cognition, language, and behavior. Cerebellar mutism in acute disseminated encephalomyelitis is rare. PATIENT: A 7-year-old boy with a 3-day history of fever, vomiting, and diarrhea presented with altered mental status and expressive aphasia. Magnetic resonance imaging showed new diffusion restriction in the bilateral dentate nuclei and right cerebellum. With treatment, he began to verbalize again but had long-term cognitive and language difficulties. CONCLUSION: Acute disseminated encephalomyelitis is commonly a benign process, but its effect on the cerebellum can be long-lasting.