Patients with chronic inflammatory bowel diseases (IBD) are at increased risk to develop osteopenia and osteoporosis. New parameters for the assessment of bone formation and especially bone resorption have significantly improved the diagnostic procedures to characterize bone metabolism. Biochemical characterization of bone turnover in IBD patients may provide important information about the pathogenesis of osteoporosis in this patient population. A cross-sectional study was performed. One hundred forty-nine patients (77 men, 52 premenopausal, and 20 postmenopausal women) with IBD (104 with Crohn's disease [CD] and 45 with ulcerative colitis [UC]) underwent clinical, osteodensitometric, and metabolic bone assessment. Bone mineral density was determined by dual energy X-ray absorptiometry. Bone formation (bone alkaline phosphatase), bone resorption (N-terminal telopeptide of type-I collagen, free desoxypyridinoline, total pyridinoline, and desoxypyridinoline), vitamin D, and parathyroid hormone were assessed. Thirty-six percent of patients with CD and 32% with UC showed osteopenia, 15% with CD and 7% with UC showed osteoporosis. Bone resorption was significantly increased in IBD patients compared to normal controls, whereas bone formation did not show a compensatory increase. Bone formation was even more suppressed in the subset of patients currently treated with corticosteroids. Our data confirm the high prevalence of osteopenia and osteoporosis reported in IBD patients. Furthermore, we provide evidence for an increased bone resorption accompanied by low bone formation in IBD patients. This imbalance of bone metabolism is likely to be one of the reasons for increased bone loss in IBD patients.