Forty-six patients with obsessive-compulsive disorder undergoing a double-blind controlled study of clomipramine and placebo were interviewed to assess changes in sexual function. Of 33 patients with previously normal organism, nearly all of the 24 on clomipramine developed total or partial anorgasmia; none of the 9 on placebo did so. Anorgasmia persisted with minimal tolerance over the five months that clomipramine was taken. Men and women were equally affected. Sexual side-effects are easily missed without a structured interview, and can detract from the value of drug treatment.