BACKGROUND: Patients with inflammatory bowel disease [IBD] including Crohn's disease [CD] and ulcerative colitis [UC] are at risk of developing metabolic bone disease. The aims here were to investigate the screening strategy, incidence and risk factors of osteoporosis in a prospective population-based inception cohort. METHOD: Between 2003 and 2004 all incident patients diagnosed with CD and UC in a well-defined Copenhagen area were included and followed until 2015. Data were compared with a control population [at a ratio of 1:20]. Regression models were performed with several covariates. The sensitivity of the Danish registries for osteoporosis was also assessed. RESULTS: A total of 513 patients were included [213 CD, 300 UC]. Overall, 338 (66%, CD: 164 [77%], UC: 174 [58%], p < 0.001] patients received ≥ 500 mg corticosteroid within a year, resulting in 781 patient-years at risk of osteoporosis. Of those, only 83 [10.6%] patient-years were followed by a dual-energy X-ray absorptiometry scan within the same or the following 2 years.Overall, 73 [14.2%] IBD patients (CD: 31 [14.6%], UC: 42 [14%]) and 680 [6.6%, p < 0.001] controls were diagnosed with osteoporosis during follow-up. The risk of osteoporosis was increased compared to the control population (odds ratio: CD: 2.9 [95% confidence interval: 2.0-4.1], UC: 2.8 [2.1-3.9]). CONCLUSION: In this population-based inception cohort, the incidence of osteoporosis was significantly higher compared to a control population. Measurement of bone mineral density is infrequent, especially in patients at high risk of developing osteoporosis. These results demonstrate the need of further awareness of the risk of osteoporosis among IBD patients, and prospective population-based studies are warranted.