The purpose of this trial is to demonstrate that a women with high body mass index (BMI > or = 28) has greater bone mineral density (BMD) from that with lower BMI. We studied 922 healthy women who met the inclusion criteria. They were classified into four groups according to their BMI (> or = 28 and < 28) and age (> or = 35 and < 35 years). Bone mineral measurement was performed by dual-energy X-ray absorptiometry (DEXA) in the hip and at the lumbar region. BMD in overweight women older than 35 years was significantly higher in comparison with that of women with lower BMI, both in the hip and the lumbar spine. In overweight women younger than 35 years, we found greater BMD in the hip reaching statistical significance, but not at the lumbar spine. We conclude that obesity is associated with greater BMD (4% at the lumbar spine; 11% at the hip) probably due to both greater physical stress and higher estrogen levels.