- Background Men with deviant sexual behavior, or paraphilia, are usually treated with psychotherapy, antidepressant drugs, progestins, and antiandrogens, but these treatments are often ineffective. Selective inhibition of pituitary-gonadal function with a long-acting agonist analogue of gonadotropin-releasing hormone may abolish the deviant sexual behavior by reducing testosterone secretion. Methods In an uncontrolled observational study, we treated 30 men (mean age, 32 years) with severe long-standing paraphilia (25 with pedophilia and 5 with other types of abnormal behavior) with monthly injections of 3.75 mg of triptorelin and supportive psychotherapy for 8 to 42 months. The efficacy of therapy was evaluated monthly by the Intensity of Sexual Desire and Symptoms Scale and yearly by the Three Main Complaints questionnaire. Results All the men had a decrease in the number of deviant sexual fantasies and desires, from a mean (±SD) of 48±10 per week before therapy to zero during therapy (P<0.001), and a decrease in the number of incidents of abnormal sexual behavior (from 5±2 per month to zero, P<0.001) while receiving triptorelin. These effects were evident after 3 to 10 months of therapy (P<0.001) and persisted in all 24 men who continued therapy for at least 1 year. The men's mean serum testosterone concentration fell from 545±196 ng per deciliter (18.9±6.8 nmol per liter) before therapy to 23±14 ng per deciliter (0.8±0.5 nmol per liter, P<0.001) after 42 months of triptorelin. The main side effects were erectile failure, hot flashes, and decrease in bone mineral density in some men. Conclusions Continuous administration of triptorelin, a long-acting agonist analogue of gonadotropin-releasing hormone, together with supportive psychotherapy, may be an effective treatment for men with severe paraphilia.