There is a paucity of treatment literature for significant and intractable behavior problems in adults with autism and mental retardation. Four adults with autism, severe to profound mental retardation, and serious, long-term behavior problems participated in an accommodation training program as an adjunct to more traditional behavioral and medical treatments. The accommodation program consisted of designing highly structured and predictable daily routines to reduce the impact of environmental factors that had previously resulted in behavior problems. Following three to six years of participation in the accommodation program, a significant treatment effect size was obtained for all participants. The benefits of this approach for improving the treatment-resistant problem behaviors and quality of life for adults with autism and mental retardation in a community-based setting are discussed as well as directions for future research. (Contains 1 table.)