Oestrogen deficiency is the main physiopathological factor of postmenopausal osteoporosis. The repercussions on bone metabolism of decrease in other sex steroid levels (progesterone, androgens) remains imperfectly known. Several studies on both animals and man have demonstrated that androgens and progestogens derived from testosterone have an anabolic effect on bone tissue. The latest data from studies conducted in non-menopausal women treated with progesterone suggest that this hormone might prevent bone loss. The mechanism of action of this effect on cells remain to be determined, even though progesterone has been shown to exert a mitogenic activity in vitro. Altogether, these data suggest that side by side with oestrogen deficiency the decrease of other sex steroid levels might also play a role in the physiopathology of postmenopausal bone loss.