The Inflammatory Bowel Disease in South-Eastern Norway study: three decades of advancements in clinical understanding and scientific partnerships.

The Inflammatory Bowel Disease in South-Eastern Norway (IBSEN) study group was initially established to ascertain the precise incidence of inflammatory bowel disease (IBD) within a specific region of Norway, thereby contributing to a global initiative aimed at elucidating the increasing prevalence of these conditions. The study was designed to foster close collaboration among national and international experts, including gastroenterologists, specialists, and private practitioners within the study area. Patients were enrolled prospectively over a 4-year period, from January 1, 1990, to December 31, 1993, based on established international diagnostic criteria and a follow-up protocol encompassing 1, 5, 10, 20, and 30-year intervals. The consortium operated through a bidirectional communication network connecting primary and secondary specialized hospitals, encompassing general hospitals and research laboratories. In 2017, the IBSEN III study was launched to facilitate a comparison of clinical and epidemiological outcomes with those of the original IBSEN study, involving an expanded catchment area and more extensive clinical and molecular assessments of the cohort. This narrative review reflects the consortium's activities through 2024 and provides comprehensive details regarding the research areas and outcomes of national and international collaborations for both IBSEN study.