The purpose of this protocol is to allow for careful screening and follow-up of patients with obsessive-compulsive disorder (OCD) and OCD-related disorders for a variety of protocols, recording demographic and rating information over the long-term course of the OCD illness and associated anxiety and depression symptoms. Patients in this study will be asked to participate in the naturalistic baseline assessment phase to better understand the pathophysiology and long-term course of illness. As a part of this protocol, subjects will be systematically administered assessment measures including diagnostic and psychological screening tests, a psychiatric assessment, SCID I and SCID II interviews, as well as other rating scales. They will also be informed of their opportunity to participate in research procedures such as blood draws and MRI of the brain. Upon conclusion of their participation, they will be referred out to community/private treatment when appropriate. All will be offered participation in an ongoing support group. This protocol will serve as an entry point for individuals with OCD and OCD-related disorders to proceed into other investigation procedures.