A family study of obsessive-compulsive disorder.

First-degree relatives of probands with obsessive-compulsive disorder (OCD) (n = 32) and psychiatrically normal controls (n = 33) were blindly interviewed with the use of the Diagnostic Interview Schedule. The morbidity risk for anxiety disorders was increased among the relatives of obsessional subjects compared with that for the relatives of controls, but the risk for OCD was not. Risk for a more broadly defined OCD (including relatives with obsessions and compulsions not meeting criteria for OCD) was increased among the parents of obsessional subjects but not among the parents of controls (16% vs 3%). The findings suggest that an anxiety disorder diathesis is transmitted in families with OCD, but that its expression within these families is variable. The findings also support the current practice of classifying OCD as an anxiety disorder.