We reviewed 45 children with cerebellar hypoplasia on magnetic resonance imaging to identify clinical features associated with cerebellar hypoplasia. We then studied children presenting with any likely associated clinical feature of cerebellar hypoplasia previously observed or reported. Two hundred fifty-one children, with one or more of these features, exhibited no cerebellar hypoplasia on imaging. We compared the children with cerebellar hypoplasia with those without cerebellar hypoplasia. Logistic regression and Pearson's chi(2) test were used. Of the 45 children with cerebellar hypoplasia, 39 exhibited developmental delay; 24, speech delay; 25, seizures; nine, microcephaly; 22, hypotonia; 22, ataxia and impaired coordination; four, abnormal movements (tremor or titubation); 13, hypertonia; eight, autistic features; and 18, ocular signs (nystagmus, strabismus, and abnormal ocular movements). Statistically significant clinical features of children with cerebellar hypoplasia compared with those without were development and speech delay, microcephaly, abnormal movements, ataxia and impaired coordination, autistic features, hypotonia, and ocular signs. The regression combination of speech delay, ataxia, hypotonia, autistic features, and ocular signs correctly predicted 86% of those with cerebellar hypoplasia. Main clinical features of cerebellar hypoplasia are developmental or speech delay, autistic features, ataxia, hypotonia, and ocular signs.