Fifty-three patients with Crohn disease were included in a prospective study. Bone mineral density was measured at the femoral neck and lumbar spine by dual-energy X-ray absorptiometry. Ten variables were analyzed in search of an association with bone demineralization; Age, sex, nutritional state, smoking, duration of the disease, hormonal status, inflammatory syndrome, site of disease: ileal, colic or ileocolic, accumulated doses of corticoids and intestinal resection. A bone demineralization was observed in 58.5% of cases. The ileum location and the corticothérapie were predictives of bone demineralization. Crohn disease is a disease at high risk of bone demineralization. Predictors of the bone loss were smoking, long duration of the disease, ileal site and systematic corticotherapy.