Sporadic nonsyndromic cerebellar hypoplasia is a radiological diagnosis with clinical features and a relation with developmental disability that are presently not known. Through a retrospective review of a comprehensive standardized computerized database containing more than 2,500 patients examined consecutively by a pediatric neurologist, 11 with nonfamilial, nonsyndromic cerebellar hypoplasia on neuroimaging (CT and/or MRI) were identified. With the exception of two patients, all had been originally referred during infancy or the preschool years for assessment of a developmental disability. All 11 had "cerebellar" findings on initial examination and five were microcephalic; three others were below the 10th percentile. All exhibited developmental disability, commonly of mild to moderate degree. Motor involvement predominated, often involving fine motor skills more than gross motor functions. Imaging consistently disclosed vermis hypoplasia with additional supratentorial cerebral dysgenesis in one child and cerebellar hemispheric hypoplasia in another. Cerebellar hypoplasia is a developmental anomaly that appears to be either etiologically related to, or a marker for, developmental disability, thus confirming the intact cerebellum's integral role in normal psychomotor development. This series suggests that cerebellar hypoplasia should be considered in the young child presenting with developmental delay with prominent motor involvement, together with cerebellar signs and/or microcephaly.