Cyproterone acetate (CPA) has been discovered more than 25 years ago and it was the first antiandrogen suitable for clinical use. CPA inhibits the action of endogenous and exogenous androgens at all androgen target organs; these include the prostate, seminal vesicles, testes, and the vas deferens. However, this antiandrogen also antagonizes less sex-specific effects of androgens, for example ossification of the epiphyseal cartilage, sebaceous gland function and skin thickness. Indications for CPA: Prostate cancer, androgen induced disorders of the skin (acne, seborrhoea, hirsutism, alopecia), precocious puberty and sexual disorders in men. Concerning sexual deviations clinical trials started in 1966. CPA leads to loss of libido and the ability to achieve erection, followed by the inability to achieve orgasm, after about 14 days of treatment (100-200 mg daily orally or 300 mg weekly i.m.). These effects are reversed in the same order as the onset. About 75 to 80% of patients respond to this therapy. CPA is generally well tolerated. Tiredness, lack of drive, listlessness and depressive moods have been reported as non-specific side-effects. Slight gynecomastia occurs in about 20% of patients. There are no good alternatives in this indication. Pure antiandrogens are unsuitable, because these are unable to inhibit libido sufficiently. Tranquilizers are not very effective, high doses of estrogens are associated with severe (cardiovascular) side effects. Orchidectomy is an irreversible intervention, LHRH analogues are associated with hot flushes and the initial increase in testosterone (flare phenomenon).