Forty men, ages 16 to 78 years, with sex-offending behavior, were treated with combined medroxyprogesterone acetate (MPA), group therapy, and individual psychotherapy. Twenty-three are pedophiles; seven, rapists; and 10, exhibitionists. Five had sex-offending behavior that began after head trauma. The duration of MPA therapy, usual intramuscular dose 400 mg/wk, ranged from six months to 12 years, usually more than two years. These men were compared with a control group of 21 men who refused MPA therapy. They had similar types of sex-offending behavior and were treated with psychotherapy alone with follow-up for a period that ranged from two to 12 years. MPA-related side effects included excessive weight gain, malaise, migraine headaches, severe leg cramps, elevation of blood pressure, gastrointestinal complaints, gallbladder stones, and diabetes mellitus. Of the 40 individuals who took MPA, 10 are still on therapy. Eighteen percent reoffended while receiving MPA therapy; 35 percent reoffended after stopping MPA. In contrast, 58 percent of the control patients, who refused and never received MPA, reoffended. Patients defined as regressed were much more likely to reoffend off therapy than the patients defined as fixated. Other risk factors for reoffense include elevated baseline testosterone, previous head injury, never forming a marriage relationship, and alcohol and drug abuse. In spite of significant medical side effects, maintenance MPA offers benefit for the compulsive sex offender by reducing the reoffense rate.