This study evaluated the effects of a behavioral summer treatment program for children with high-functioning autism spectrum disorder (HFASD). Twenty boys (M = 9.2 years) diagnosed with HFASD participated in the 6-week program across 6 years. Detailed daily behavioral data were collected on a variety of positive and negative social behaviors. Repeated measures ANOVAs of weekly behavior frequencies indicated substantial improvements in a number of behaviors over the 6 weeks of the program, including following activity rules, contributing to a group discussion, paying attention, and less complaining/whining. Overall, results highlight the potential efficacy of treating chronic functional impairments of HFASD and associated problem behaviors in the context of an intensive behavioral summer treatment program.