 Autism is a complex neurodevelopmental disorder that is thought to involve an interaction between multiple and variable susceptibility genes, environmental factors, and epigenetic effects. Great concern has been raised about the marked increase in the prevalence of autism spectrum disorders in the last decade. Risperidone, the most studied atypical antipsychotic used in children, has been shown to improve severe behavioral difficulties in over half of children with autism who have these difficulties. However, not all children with autism and severe behavioral problems respond to risperidone, and for a few, it has significant side effects. 