Bone mineral density (BMD) is reduced in the distal radius, proximal femur and lumbar spine of hypogonadal individuals. The objective of the present cross-sectional study was to assess cranial BMD by dual energy X-ray absorptiometry in patients with hypogonadism arising during the first two decades of life, submitted or not to hormone replacement, as well as in menopausal women not submitted to hormone replacement. Cranial BMD was significantly lower in hypogonadal without treatment (1.656 + 0.24 g/cm2; mean + SD) when compared to normal young individuals (1.996 + 0.17). The cranial bone mass did not differ significantly between untreated and treated young hypogonadal individuals (1.779 + 0.32 g/cm2). The values detected in both groups were significantly lower than those detected in the menopausal women (2.146 + 0.29 g/cm2; p<0.01). The cranial BMD of patients with primary hypogonadism did not differ from that of patients with central hypogonadism and confirmed growth hormone deficiency (1.654 + 0.23 versus 1.601 + 0.16 g/cm2). We conclude that hypogonadism of early onset is associated with a marked reduction in cranial BMD, a finding probably due to the high sensitivity of trobecular bone to sex steroid deficiency and to the interference of this deficiency with the achievement of bone mass peak.