This study investigates response inhibition deficits in obsessive-compulsive disorder (OCD) by using the Hayling task. Sixteen OCD washers, 16 OCD checkers, 16 social phobic patients and 16 nonanxious controls were asked to complete sentences with either the expected word (section A: “initiation”) or an unrelated word (section B: “inhibition”). The groups did not differ in terms of section B minus section A latencies. However, OCD washers and checkers made significantly more errors (sentence-related responses) in section B than social phobic patients and controls. In the OCD patients, the frequency of these errors correlates with the total OCD severity score and the compulsion subscore, but not with the depression and anxiety scores. These findings suggest that OCD patients might present a specific deficit affecting the inhibition of a prepotent response. (JINS, 2005, 11, 776–783.)