The proposed study attempts to deepen our understanding of repetitive behaviors in autism spectrum disorders (ASD) and its treatment by examining the changes in key neural circuits associated with risperidone treatment using functional MRI. This study is a substudy of a larger center grant (IRB#07-03-066). Other studies also under this center grant, include: IRB#03-02-085, IRB#95-01-028. All participants will have the option to enter another sub-study, should they meet criteria. The proposed study will address this aim by mounting a controlled trial of 52 children with Autism Spectrum Disorder. After screening assessment, children will enter a three-part study. Phase 1 will be an 8-week, double-blind, placebo-controlled flexible dose trial of risperidone. The extension phase is a 16-week open-label maintenance phase for responders to risperidone or placebo. Non-responders to placebo will be invited to enroll in the eight-week open-label study. 48 of the participants will also undergo fMRI at Week 8 while on blinded treatment, as an optional sub-study. The medication will be dispensed in a liquid suspension and the dose will range from 0.5 mg to 4.0mg.