Twenty six children with autism, 24 children with developmental disabilities, and 15 typically developing children participated in tasks in which an adult displayed emotions. Child focus of attention, change in facial tone (i.e., hedonic tone), and latency to changes in tone were measured and summary scores of emotional contagion were created. Group differences existed in the ratio of episodes that resulted in emotional contagion. Correlations existed between measures of emotional contagion, measures of joint attention, and indices of severity of autism. Children with autism demonstrated muted changes in affect, but these responses occurred much less frequently than in comparison groups. The findings suggest directions for early identification and early treatment of autism.