Previous studies have confirmed that the prevalence of decreased bone mineral density is elevated in patients with inflammatory bowel disease. The objective of the current study was to determine the prevalence of osteopenia and osteoporosis in a cross-sectional outpatient population of 242 adult patients with Crohn's disease and to determine which clinical characteristics and serum and urine biochemical factors might be predictive of bone loss. Thirty-seven percent had normal bone density, 50.0% were osteopenic, and 12.9% were osteoporotic. Among the sites used to diagnose low bone mineral density, the femoral neck demonstrated the highest prevalence of osteopenia and the ultra-distal radius the highest prevalence of osteoporosis. However, low bone mineral density at one site was always predictive of low bone mineral density at the other. Corticosteroid use during the year before assessment was found to be consistently predictive of low bone mineral density in males but not in females. In contrast, low body mass index and high platelet counts were consistently predictive of low bone mineral density in females but not in males. Disease location, smoking, and age were not predictive of changes in bone mineral density.