 Blood genomic profiles are shown to predict medication response for disorders such as cancer and epilepsy. This exploratory or discovery study will use blood genomic profiles before and after risperidone treatment in children with autism and severe behavioral difficulties to determine if the profiles can predict response to treatment. The ultimate goal of this line of research is to develop methods to predict which medications work for which child before initiating treatment, to predict which child might develop particular side effects, and to identify new treatment targets for future medication development. 