Pervasive developmental disorders are characterized by lifelong impairments in fundamental social and/or communication skills and by the presence of seemingly purposeless and repetitive behaviors, interests, or activities. A number of possible biological etiologies, including genetic, structural and functional brain abnormalities, have been identified in patients with pervasive developmental disorders. In addition, clinicians should take the possibility of comorbid psychiatric conditions into consideration when making the differential diagnosis of pervasive developmental disorders.