The role of sex hormones in the sexuality of men is now becoming clearer. Androgens are necessary for normal sexual appetite and for ejaculation. Erectile mechanisms, providing that appropriate erotic stimuli are available, are probably not androgen dependent. How much testosterone is required to obtain maximum sexual effect is not yet clear but it probably varies from individual to individual and may be well within the normal range in some men. Androgens may therefore be beneficial in treating loss of sexual appetite in men but are unlikely to improve erectile dysfunction unless it is secondary to loss of sexual appetite. In women the picture is much less clear. Apart from the estrogen dependence of the vaginal epithelium, important for the postmenopausal woman, female sexuality shows a very unpredictable relationship with reproductive hormones. Possible reasons for this variable picture are discussed, in particular a greater genetic variability and behavioral sensitivity to hormones in women than in men.