Additional Study Information: The goal of the project is to identify brain characteristics associated with obsessive-compulsive disorder (OCD) by comparing brain images of (1) individuals with OCD, (2) individuals without OCD, and (3) siblings of individuals with OCD who do not themselves have the disorder. Eligible participants will be asked questions about their medical and psychiatric history, perform tasks on a computer, and receive a brain scan using Magnetic Resonance Imaging (MRI). The study can be completed in one or two in-person visits. This study does not involve treatment. Participants will be compensated for their time and effort.