Bone mineral density in cortical (BMDd) and trabecular parts (BMDud) of the distal forearm was studied in 494 healthy subjects ranging from 8 to 17 years with single photon absorptiometry. Mean BMDd was 6.8% higher (p < 0.0001) in boys than in girls in the < 11 years age group (n = 163). Mean BMDud was 8.2% higher (p < 0.0001) in boys than in girls in the adolescent age group (> or = 11 years, n = 331). While BMDd increased from 11 years of age in girls and was delayed by 2 years in boys, BMDud increased from 10 years of age in boys and was delayed by 1 year in girls. By multiple regression analysis, age, weight and height were variably related to bone density depending on measuring site, sex and age. At 14 years of age, postmenarcheal girls had obtained BMDud values similar to those of an adult premenopausal group. Cortical bone density in girls was very close to corresponding BMDd values of the adult premenopausal group at 16 years of age. In conclusion, this cross-sectional study indicates sex and age variability in forearm bone mineralization at trabecular and cortical sites. The substantial mineralization taking place between 11 and 16 years of age, with achievement of adult premenopausal bone density values, makes this 5-year period crucial for bone development.