Four demented male patients who manifested disruptive sexual behavior, including public masturbation and attempts to molest female patients, and who could not be managed by other means received a therapeutic trial of medroxyprogesterone acetate (MPA) for 1 year and were followed up for an additional year. Their sexual activities were recorded before, during, and after the study, and serum testosterone, luteinizing hormone (LH), and prolactin were monitored regularly. Within 2 weeks of the start of MPA therapy, the sexual acting out had stopped; this was associated with a 90% and a 60% decline, respectively, of serum testosterone and LH. When MPA treatment was stopped, testosterone and LH returned to pretrial levels in all four men. One showed a return of sexual acting out, but this was at a reduced level and was successfully managed by firm nursing. MPA was used without adverse effects. Because of its safety and efficacy, the drug should be considered as a first-line treatment for sexual acting out in demented men.