Relationships between bone mineral density (BMD) and body mass, height, fat mass, and lean mass have been reported. This study examined the relationship between body size and composition on bone density in young premenopausal women. In this study, a cross-sectional design was used. Seventy-one healthy women aged between 24 and 36 yr selected to have a wide range of boy habitus (mean body mass index, 22.7 +/- 3.0) underwent a dual-energy X-ray absorptiometry (DXA) whole-body bone density scan (Hologic QDR 2000). Their bone density and soft tissue body composition and anthropometric parameters (skinfolds, girths, limb lengths, bone breadths, height, and body mass) were analyzed, and their body cornposition was assessed by underwater weighing (UWW). Bone-free lean mass (BFLM) determined by DXA was correlated with both bone mineral content (BMC) and BMD (r = 0.74, p < 0.001; r = 0.48, p < 0.001, respectively). In addition, fat-free mass (FFM) determined by UWW was correlated with BMC and BMD (r = 0.80, p < 0.001; r = 0.48, p < 0.001, respectively). Controlling for height in the model removed most of the correlations with whole-body BMD, with the exception of FFM, BFLM, and shoulder breadth (r = 0.39, p < 0.001; r = 0.37, p < 0.01; and r = 0.34, p < 0.01, respectively). No correlation was found between fat mass by DXA, UWW, and sum of skinfolds and BMD. These results indicate that bone mass in premenopausal women is dependent on lean body mass.