Obsessive-compulsive disorder (OCD) is a common psychiatric illness. People with OCD experience unwelcome thoughts, known as obsessions, and feel compelled to perform repetitive behaviors, or compulsions. Impairment due to OCD symptoms ranges from mild to severe, and sometimes can be disabling. The only medications proven effective for OCD are serotonin reuptake inhibitors (SRIs), but even with SRI treatment, most patients continue to experience significant OCD symptoms, impaired functioning, and diminished quality of life. Cognitive-behavioral therapy (CBT), a talking therapy that focuses on altering a person's thoughts and behaviors, and the medication risperidone have both been commonly used for augmenting SRI treatment for OCD. This study will compare the short- and long-term effectiveness of exposure and ritual prevention (EX/RP), a type of CBT, and risperidone in augmenting SRI treatment in people with OCD.