Challenging behaviors were assessed in 313 children, and it was demonstrated that children with autism spectrum disorders (ASD) exhibited greater levels of challenging behavior than both normally developing controls and children with psychopathology or atypical development. Next, we examined the relation between challenging behaviors and symptoms of autism in children with ASD. Severity of ASD was positively related to the number and intensity of challenging behaviors, and those with severe ASD exhibited significantly higher levels of problem behaviors than children with mild or moderate ASD. In addition, clusters of ASD symptoms were able to accurately predict endorsements of 8 of the 18 challenging behaviors assessed. Implications for the assessment and intervention of ASD and challenging behaviors are discussed. (Contains 4 tables.)