The purpose of this study was to measure the bone mineral density of the lumbar spine (L(2)-L(4)) in healthy postpartum women following term delivery, and to evaluate factors associated with bone mineral density. Using dual energy X-ray absorptiometry, the bone mineral density of the lumbar spine was determined during 1 year in 123 healthy postpartum Japanese women following term delivery. The mean bone mineral density of the lumbar spine was 1.007 +/- 0.108 g/cm(2) (range 0.731-1.252 g/cm(2)). Thus, there were wide interindividual differences. Also, this result was in agreement with the peak bone mass previously reported for other Japanese women. Multiple regression analysis and linear regression analysis showed that weight and body mass index were each significantly correlated with bone mineral density of the lumbar spine. Age, parity, height, and baby's birth weight were not contributory.