To assess the rate of bone loss in patients with inflammatory bowel disease, we prospectively studied 35 patients (17 women) aged 36 +/- 13 (range 17-60) years, 14 of whom had Crohn's disease and 21 with ulcerative colitis (including 12 with ileoanal anastomosis). Bone mineral density was measured by dual-energy X-ray absorptiometry at the lumbar spine and femoral neck. The follow-up was 19 +/- 8 months. During this period, 14 patients received oral steroids. Lumbar bone density changes expressed as a percentage per year were -3.1 +/- 4.9%, -6.4 +/- 7.5% and +2.0 +/- 4.0% in Crohn's disease and ulcerative colitis without and with ileoanal anastomosis respectively (p = 0.007). The same pattern was observed at the femoral neck. Mean annual lumbar bone density changes were -6.2 +/- 7.0% and +0.9 +/- 3.9% in patients with and without steroids during follow-up (p = 0.002). We conclude that patients with inflammatory bowel disease are at risk of lumbar and femoral bone loss. However, bone loss is not observed in patients with ileoanal anastomosis.