BACKGROUND: It remains uncertain whether the increasing incidence of inflammatory bowel disease (IBD) during the last decades has been accompanied by an alteration in the presentation, course, and prognosis of the disease. To answer this question, 3 consecutive population-based IBD cohorts from Copenhagen, Denmark (1962-2005), were assessed and evaluated. METHODS: Phenotype, initial disease course, use of medications, cumulative surgery rate, standardized incidence ratio of colorectal cancer (CRC), and standardized mortality ratio (SMR) were compared in the 3 cohorts, which had a total of 641 patients with Crohn's disease (CD) and 1575 patients with ulcerative colitis (UC). RESULTS: From 1962 to 2005, the proportion of IBD patients suffering from CD increased (P < 0.001), time from onset of symptoms to diagnosis of CD decreased (P = 0.001), and median age at diagnosis of UC increased (P < 0.01). The prevalence of upper gastrointestinal involvement and pure colonic CD varied significantly between cohorts. UC patients diagnosed in the 1990s had a higher prevalence of proctitis, received more medications, and had a milder initial disease course than did previous patients. The surgery rate decreased significantly in CD but not in UC. The risk of CRC in IBD was close to expected over the entire period, whereas the mortality of patients with CD increased (overall SMR, 1.31; 95% CI, 1.07-1.60). CONCLUSIONS: Despite variations in the presentation and initial course of IBD during the last 5 decades, its long-term prognosis remained fairly stable. Treatment of IBD changed recently, and future studies should address the effect of these changes on long-term prognosis.