To elucidate the pathology of osteoporosis associated with rheumatoid arthritis (RA), bone mass measurements were performed in 146 female patients with RA and compared with those in 150 age-matched female patients with osteoarthritis (OA) and postmenopausal osteoporosis (OP). Bone mineral density (BMD) was measured at the lumbar spine (L-BMD), the mid-radius (MR-BMD) and the calcaneus (C-BMD) by dual-energy X-ray absorptiometry (DXA), and at the distal radius by peripheral quantitative computed tomography (pQCT). The RA group showed significantly lower BMD at all sites, except L-BMD, than the OA group. Compared with the OP group, the RA group showed a significantly higher L-BMD but no difference at other sites. BMD in RA decreased with disease severity at all sites and lean body mass was highly correlated with L-BMD and C-BMD. Cross-sectional analysis revealed early bone loss at the distal radius and a decrease of L-BMD, MR-BMD, and C-BMD with disease duration. Longitudinal analysis showed that the annual loss of L-BMD, MR-BMD and C-BMD tended to be lower with increasing disease duration. Glucocorticoid administration had no influence on L-BMD, MR-BMD or C-BMD. We concluded that, unlike postmenopausal osteoporosis, osteoporosis associated with RA is characterised by relatively preserved bone mass in the axial bone and marked loss in the peripheral bone. The risk factors for generalised osteoporosis are a long disease duration, severity of disease, and decreased lean body mass.