Fear of inducing generalised osteoporosis is one reason why corticosteroids are withheld in patients with rheumatoid arthritis (RA). No studies, however, have directly measured bone density in such patients at clinically relevant sites. To assess this risk we measured bone mineral density in the lumbar spine and femoral neck by dual photon absorptiometry in 84 patients with RA, 44 of whom had been treated with low dose prednis(ol)one (mean dose +/- SE 8.0 +/- 0.5 mg/day; mean duration of treatment 89.6 +/- 12.0 months). There were significant reductions in bone mineral density in patients treated with corticosteroids (lumbar 9.6%, p less than 0.001; femoral 12.2%, p less than 0.001) and in those who had not received corticosteroids (lumbar 6.9%, p less than 0.01; femoral 8.9%, p less than 0.001), but the differences between the two groups were not significant. We conclude on the basis of these studies that low dose oral corticosteroids do not increase the risk of generalised osteoporosis in patients with rheumatoid arthritis.