Rates of challenging behaviors were assessed in 175 adults with intellectual disability (ID) or ID and a comorbid autism spectrum disorder (ASD). The relationship between ASD diagnosis, race, and challenging behaviors was assessed using the "Autism Spectrum Disorders-Behavior Problems for Adults (ASD-BPA)." Those with ASD and ID were found to exhibit significantly more challenging behaviors than those with ID alone. No significant main effect of race was found. However, a significant interaction between ASD diagnosis and race was found: In those with ASD, Caucasian participants exhibited more challenging behaviors than African Americans, whereas the opposite held true in those without ASD. Specific subscales of the ASD-BPA were also examined, with a significant interaction found on the Stereotypy subscale. Results and their implications are discussed. (Contains 2 tables and 1 figure.)