Androgen deprivation therapy (ADT) for prostate cancer (PCa) treatment causes sexual dysfunction. We review here the effects of estrogen on the sexual performance of androgen-deprived males. The major findings are: 1. Estrogen receptors are present in brain centers that are important for sexual behavior; as well as in male reproductive organs, in a pattern suggesting that estrogen may have some role in orgasmic function and genital skin sensitivity. 2. Estrogen restores sexual interest above castrate levels in many vertebrates including reptiles, birds and mammals; but multiple factors contribute to the magnitude of this effect. 3. Data from castrated men, aromatase-deficient men, male-to-female transsexuals, and men on antiandrogens all suggest that estrogen can maintain some libido in androgen-deprived men. We discuss the general benefits of estrogen therapy to quality of life of men on ADT, the potential risks of this treatment, and possible treatment regimes for estrogen therapy in males. Unless contraindicated, we propose that PCa patients on ADT would benefit from supplemental parenteral estrogen.