A wide range of psychiatric and medical disorders have been hypothesized to be related to obsessive compulsive disorder (OCD) and thus, together, to form a family of disorders known as obsessive compulsive (or OCD) spectrum disorder. The grouping of these conditions is based on their phenomenological similarities with OCD (i.e., obsessive thinking and/or compulsive behaviors), as well as their having courses of illness, comorbidity and family history patterns, biological abnormalities, and treatment responses similar to OCD. Proposed OCD spectrum disorders have included body dysmorphic disorder, hypochondriasis, anorexia nervosa, trichotillomania, and some forms of delusional disorder, among others. However, conditions with impulsive features have also been hypothesized to belong to this family, including impulse control disorders in general, paraphilias and nonparaphilic sexual addictions, bulimia nervosa and binge eating disorder, and Tourette's disorder. We review the evidence supporting the grouping of these conditions into an OCD spectrum disorder family. We conclude that these disorders are different in some ways from OCD, but that they also have many similarities with OCD, and may therefore be related to one another and to OCD. In addition, we hypothesize that some of the differences among them may be explained in part by variation along a dimension of compulsivity versus impulsivity. Finally, because most of these conditions appear to be related to mood disorder, we hypothesize that the OCD spectrum disorder family may belong to the larger family of affective spectrum disorder.