To assess the prevalence and risk factors for low bone mineral density in inflammatory bowel disease, we studied 61 consecutive patients, mean age 36 +/- 11 years. Twenty-seven had a Crohn's disease and 34 ulcerative colitis (including 13 with ileoanal anastomosis). Three patients, two women and one man (32, 70, and 45 years old, respectively) had vertebral crush fractures. Bone mineral density measured by dual energy x-ray absorptiometry at spine and femoral level was more than 2 SD below normal values in 23% of the patients, all of them having received steroid therapy. Eighteen patients (29%) had never received steroid therapy; their bone mineral density was not different than those who had. Univariate analysis showed a positive correlation between bone mineral density and body weight or oral calcium intakes, and a negative correlation with steroid daily dose. After ileoanal anastomosis, bone mineral density was not different from other groups and showed a positive correlation with time elapsed since coloproctectomy. We concluded that bone mineral density is low in patients with inflammatory bowel disease and exposes them to the risk of bone fracture. Bone mineral density after ileoanal anastomosis may increase with time after surgery.