We compared two functional behavioral assessment methods: the Questions About Behavioral Function (QABF; a standardized test) and experimental functional analysis (EFA) to identify behavioral functions of aggressive/destructive behavior, self-injurious behavior and stereotypy in 32 people diagnosed with autism. Both assessments found that self injurious behavior (SIB) was mostly maintained by automatic reinforcement and escape from task demands. Aggressive/destructive behavior was found to be maintained by escape and access to tangibles, whereas stereotypy was mostly maintained by automatic reinforcement. There was exact agreement on function(s) between the two assessments for 24 participants and partial agreement for six participants. Results suggest that the QABF has clinical utility and is an effective tool for ascribing behavioral function. Implications of the present findings for future assessment of behavioral function are discussed. (Contains 4 figures and 7 tables.)