A sample of 181 healthy premenopausal Caucasian women, 20 to 50 years of age, was part of a cross-sectional study on the determinants of radial bone mineral content (BMC), bone width (BW) and areal bone mineral density (BMD) at two sites, the distal (Dis) or 5 mm-site (about 50% cancellous tissue) and the mid-radial (Mid) site (over 90% cortical tissue), as measured by single photon-absorptiometry. Women in their 20s (n = 45) had significantly lower DisBMC and DisBW values than women in their 30s (n = 65) or 40s (n = 71). No such trends were noted for any of the mid-radial measurements with increasing age. With age, height and weight included in the same regression equation, age remained the only significant positive predictor of all three distal variables, while height was the only significant positive predictor of the mid-radial variables. Body weight was not associated with any of the bone variables in this model. A low lean body mass (LBM) or low body mass index (BMI) was consistently correlated with significantly lower bone values at both radial sites. These data suggest that peak bone mass (PBM), for the distal and largely cancellous portion of the radius, was achieved later in adulthood (30s) than the mid-radial or mostly cortical portion of the radius in which PBM was achieved much earlier, probably in late adolescence.