Risperidone, the most studied atypical antipsychotic used in children, has been shown to improve severe behavioral symptoms in over half of children with autism with these problems. However, not all children with autism and severe behavioral problems respond to risperidone, and for a few, it has significant side effects. Blood genomic profiles are shown to predict medication response for disorders such as cancer and epilepsy. This study will use blood genomic profiles before and after risperidone treatment in children with autism and severe behavioral problems 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.