The extent to which parents of children with intellectual or developmental disabilities are adherent to prescribed treatments has not been investigated. In this treatment adherence study, parents (n = 220) of children with autism spectrum disorders were surveyed regarding implementation of recommended treatments to manage problem behavior of their children living at home. Overall adherence to medical treatment recommendations was significantly greater than adherence to behavioral treatment recommendations (p less than 0.002). Of the behavioral treatment recommendations, parents reported greater adherence to reinforcement (81.7%) than punishment (68.9%). Child diagnosis (p less than 0.002) and the diagnosis x marital status interaction (p less than 0.05) were significantly associated with reported adherence to behavioral and medical treatment, respectively. Results are discussed in light of the need to address adherence enhancement and measurement methods.