Summary To assess the influence of puberty and its associated changes in body weight and height on bone mineral density (BMD), lumbar spine (L2–L4) and femoral neck BMD were measured in 74 healthy, active children (9–16 years) using dual-photon absorptiometry. Competitive swimmers were recruited to minimize the potential effect variability in mechanical loading regime may have on bone density of the lumbar spine. Tanner staging was wed to assess stage of puberty. Current dietary calcium intake was assessed by analysis of 6-day dietary records. Significant differences in spinal and femoral neck BMD occurred between early (Tanner 1 and 2) and late stages of puberty (Tanner 4 and 5), P < 0.05. A significant correlation was found between bone density and dietary calcium intake. However stepwise regression analyses demonstrated stage of puberty or body weight were the only factors which significantly affected spinal BMD, accounting for 77% and 68% of the variability respectively; while at the femoral neck, body weight accounted for 52% of the variability. These results demonstrate that when potential interacting factors are controlled for through regression analyses, differences in BMD occur mainly as a function of puberty and the associated gains in body weight.