Intermittent endocrine treatment or cyclic therapy of prostate cancer aims at prolonging survival by delaying progression to androgen independence and at improving quality of life by avoiding the side effects of continuous androgen ablation. In this paper we first review the available experimental data suggesting the clinical application of this therapeutic strategy and interpret them with caution. We then examine the published reports of phase II clinical studies showing the feasibility of this approach. Intermittent endocrine treatment is capable of inducing multiple apoptotic regressions; improvement in the sense of well-being and quality of life - including sexual function - is regularly reported. A period of 6-9 months on therapy is usually recommended; the mean off-therapy interval approaches 50% of the duration of the treatment cycle. The mean time to disease progression was 32 months. The definitive answer to the important question of prolonged survival awaits the completion of ongoing randomized studies.