Six patients with severe paraphilia were treated with a long-acting gonadotrophin hormone releasing hormone analogue (GnRH-a). In five cases, the antiandrogen treatment ended their deviant sexual behaviour and markedly decreased their sexual fantasies and activities without significant side-effects. The beneficial effects of this treatment were maintained for 7 years in the patient where there was the longest follow-up. Two patients abruptly withdrew front their antiandrogen treatment at the end of the first and third year, respectively. Both relapsed within 8-10 weeks. One of them asked for resumption of antiandrogen treatment. In another case, in order to phase out antiandrogen treatment, testosterone (T) was added to the GnRH-a. In spite of normal T levels, and of resumption of normal sexual activities and deviant fantasies, deviant sexual behaviour did not return. A smoother phasing out of GnRH-a treatment is thought to be better than an abrupt withdrawal. However, the duration of antiandrogen treatment necessary to ensure a complete disappearance of deviant sexual behaviour remains uncertain, but is at least 4 years.