In males, estrogens are synthetized in peripheral tissue by aromatization of testosterone. Recent data show that males either with a non functional estrogen receptor or unable to synthetize estrogen have osteoporosis although they have normal circulating levels of androgens. Several transversal studies show that, in aged males, estrogens are better correlated to bone density than androgens. Free estradiol and free androgen levels are both decreased during ageing between 50 and 80 years old. Estrogen rather than androgen deficiency is responsible of increased bone resorption in aged males. So far there is no treatment without side effect for the treatment of estrogen deficiency in males.