We report two children who were referred for diagnostic assessment for autism and were subsequently determined to have a muscular dystrophy (MD). Each child had a history of speech delay and social impairments, but also had motor delays that had not previously been investigated. Both children met diagnostic criteria for autism spectrum disorders on standardized assessment. Each child was hypotonic and had other mild motor impairments. Serum creatine kinase (CK) activity was markedly elevated in each child, and subsequent muscle biopsy led to diagnosis of Becker's MD and congenital (autosomal recessive) MD, respectively. These cases highlight the importance of a thorough neuromotor examination for all children with suspected autism spectrum disorders.