Obsessive-compulsive (OC) symptoms are often present among youth with Prader-Willi Syndrome (PWS). They are also associated with considerable problems in the daily functioning of the child and his/her family. Although medication and behavioral treatments exist that target OC symptoms among youth without PWS, these treatments have not been thoroughly adapted for this population nor scientifically tested. Although medication has been helpful in addressing OC symptoms in several published case reports, the associated efficacy is modest and the potential for side effects is a realistic concern. Given that behavioral treatment for OC symptoms has superior efficacy to pharmacotherapy in youth without PWS without the accompanying risk for adverse side effects, it follows that an adapted version of behavioral therapy may hold promise in treating clinically problematic OC symptoms in youth with PWS. Thus, the purpose of the proposed grant is to develop and pilot-test a behavioral treatment for OC symptoms for use in youth with PWS. This study will allow us to develop and test a treatment protocol aimed at reducing OC symptoms that are clinically problematic and negatively impact functioning and quality of life in the child and his/her family.