Recent reports in the literature have suggested a link between abnormalities of the cerebellar vermis and the behavioral syndrome of autism. Joubert syndrome is an autosomal recessive disorder characterized by partial or complete agenesis of the cerebellar vermis. However, there is little behavioral or psychiatric description of patients with this genetic condition. In this report, the neuropsychiatric characteristics of two children with Joubert syndrome are described in detail. One child met DSM-III-R diagnostic criteria for autistic disorder, while the other displayed autistic features. The female child displayed stereotypic behavior and impairments in social interaction and communication, had a markedly restricted repertoire of interests, and showed distress over changes in the environment. The male child demonstrated perseveration and preoccupation with sounds and textures, but had no abnormalities in social interaction. Although both children showed developmental disabilities, the degree of cognitive delay was significantly less than that described in previous reports of children with Joubert syndrome. This report adds to the growing body of evidence implicating cerebellar involvement in developmental disabilities and autistic behavior.