Maximizing peak bone mass is advocated as a way to prevent osteoporosis. As a prerequisite to the elaboration of any preventive program aimed at maximizing peak bone mass, it is important to determine how the rate of skeletal growth at clinically relevant sites, such as lumbar spine and femoral neck, proceeds in relation to age and pubertal stages in both sexes. Bone mass was assessed in 207 healthy caucasian boys and girls, aged 9-18 yr. Bone mineral density (BMD; grams per cm2) and content (BMC; grams) were determined in lumbar spine (L2-L4), femoral neck (FN), and midfemoral shaft (FS), using dual energy x-ray absorptiometry. Bone variables were correlated with both chronological age and pubertal stage, and compared with young adult (20-35 yr) reference values. The main results are: 1) in males, compared to females, there was a marked age-related delay in L2-L4 BMD or BMC increase, but no delay was observed in relation to pubertal stages; 2) at the end of the rapid growth spurt, trends for higher mean values in males were observed for L2-L4 BMC, FN BMD, and particularly FS BMD, but no sex difference was observed for L2-L4 BMD; 3) in females, but not in males, a dramatic reduction in bone mass growth was observed after 15 yr of age, particularly for L2-L4 BMD/BMC and FN BMD. This sharp reduction occurred between the second and fourth years after menarche. In the 14- to 15-yr-old female group, BMD in L2-L4, FN, and FS corresponded to 99.2%, 105.1%, and 94.1%, respectively, and BMC in L2-L4 to 97.6% of the mean values recorded in 20- to 35-yr-old women. In conclusion, this cross-sectional study indicates that during pubertal development, major differences are observed in bone mass growth according to sex and skeletal site. Whereas in males bone mass at different skeletal sites continues to increase substantially between 15-18 yr, skeletal mass growth appears to dramatically slow down at the levels of both lumbar spine and FN at 15-16 yr of age in female adolescents. This suggests that the generally accepted notion that in both males and females bone mass continues to substantially accumulate at all skeletal sites until the fourth decade may not be a constant in human physiology.