A study of 73 consecutive children with acute cerebellar ataxia seen over a 23 year-period is reported from the Departments of Pediatrics and Neurology, Washington University School of Medicine and St Louis Children’s Hospital. Mean age at onset was 5 years (range, 1 to 21 years); 60% were 2 to 4 years at onset. Prodromal illnesses identified in 57 children included chicken pox in 26%, other presumed viral illness in 52% and immunization related in 3%. No prodrome was recognized in 19%. Epstein-Barr virus was identified in 2 children. Gait ataxia was most severe in patients with varicella, EBV, and vaccination. Other neurologic abnormalities included dysmetria, nystagmus, cranial nerve palsies, and corticospinal tract signs. WBC counts were elevated in half the postviral ataxia cases and normal in the remainder. CSF protein averaged 24 mcg/dl and the mean WBC count was 10 (range, 0-107/mm³). Pleocytosis >5 was present in one half. Brain scans were normal with one temporary exception. Recovery was complete in 91% of 60 followed for 4 months or longer; 100% in post-varicella cases and 89% in children with non-varicella-related ataxia. Transient behavioral or intellectual difficulties occurred in 20%, and learning problems persisted in 5 (8%). Four children had recurrences of acute ataxia, usually after another presumed viral illness. [1]