Both cognitive impairment and autism are common in the tuberous sclerosis complex, but the relationship between the 2 diagnoses has not been formally explored. The authors evaluated 20 clinic-referred children with tuberous sclerosis complex at ages 18, 24, 36, and 60 months and classified them as autism, autism spectrum disorder, or normal on the basis of the Autism Diagnostic Observation Schedule. Using the Mullen Scale of Early Learning, cognitive function in each subgroup was assessed. The authors then analyzed the subscores of the Autism Diagnostic Observation Schedule in children with autism. Children with autism showed significantly more global cognitive impairment than those without autism. In addition, all children had some baseline cognitive impairment and the majority had deficits in play scores. The authors conclude that clinic-referred children with tuberous sclerosis complex and autism are at considerable risk for cognitive impairment. These characteristics may help to guide more tailored services for these high-risk children.