Generalised osteoporosis is a feature of established rheumatoid arthritis but whether this is a consequence of treatment, immobility, or disease activity has been unclear. We estimated bone mineral density by dual energy x-ray absorptiometry on 148 patients with early rheumatoid arthritis before treatment with corticosteroids or disease-modifying drugs and 730 normal controls. Scans were done at 12-month intervals in patients and at 0 and 12 months on 50 of the controls matched for menopausal status. At presentation, bone mineral density of patients did not differ from controls. However, patients with disease for less than 6 months had significantly higher spinal bone mineral density than those of longer duration. Over the next 12 months, bone mineral density loss was greater in patients with rheumatoid arthritis compared with controls; significantly so for early disease (eg, -2.4 [0.8] vs -0.6 [0.4] g/cm2, p < 0.05 in the spine and -4.3 [0.8] vs -0.4 [0.5] g/cm2, p < 0.001 in the trochanter). For the lumbar spine, only disease activity was significantly associated with this bone mineral density loss. For patients with active disease over 2 years, mean bone mineral density loss at each site was between 5.5 and 10% (p < 0.01 compared to patients with inactive disease). Suppression of disease activity stabilised this bone loss. In patients with rheumatoid arthritis significant amounts of generalised skeletal bone were lost early in the disease and the loss was associated with disease activity. These findings have implications for the management of patients with rheumatoid arthritis and possibly other inflammatory diseases.