Book excerpt: While other texts provide general information on obsessive-compulsive disorder (OCD), this is the first book to make a wider, inclusive examination of the disorders that appear to be closely linked to OCD (i.e., body dysmorphic disorder, trichotillomania, Tourette's syndrome, etc.) and review the diagnostic, biological, and treatment issues surrounding their relationship. Obsessive-Compulsive Related Disorders discusses the way compulsivity and impulsivity are studied and understood in the diagnosis and treatment of these obviously related disorders -- should they be diagnosed by categories, or in the context of dimensional models? Subsequent chapters also examine serotonin's role in these psychiatric disorders.