Several clinical investigations with adults suggest that the cerebellum may be critical for judgment of explicit time intervals; however, little work has been done in populations with lesions of the cerebellum acquired during development. We evaluated 17 individuals with ataxia-telangiectasia (AT), an autosomal recessive disorder with on-set in early childhood characterized by diffuse, almost selective, degeneration of the cerebellar cortex, and 21 normal controls, matched for age. Because patients with AT have motor impairment, verbal IQ (VIQ) was used to estimate intelligence; VIQ was significantly lower in the group with AT (p < .0001). Participants were tested using a test of judgment of duration that has been found to be impaired in adults with cerebellar lesions and a contrasting auditory control task (not impaired in adults with cerebellar lesions) involving judgment of pitch. After statistically controlling for VIQ, the 2 groups did not differ significantly on judgment of pitch, but those with AT performed significantly worse than controls on judgment of duration (p = .01). Children and adolescents with AT show deficits in judgment of duration but not of pitch, suggesting that the cerebellum may be critical for judgment of explicit time intervals at all ages.