Objective: To determine dysplasia and cancer in the 1991-2004 European Collaborative Inflammatory Bowel Disease (EC-IBD) Study Group cohort. Patients and Methods: A patient questionnaire and a physician per patient form were completed for each of the 1,141 inflammatory bowel disease patients (776 ulcerative colitis/365 Crohn's disease) from 9 centers (7 countries) derived from the EC-IBD cohort. Rates of detection of intestinal cancer and dysplasia as well as extra-intestinal neoplasms were computed. Results: Patient follow-up time was 10.3 +/- 0.8 (range 9.4-11) years. The mean age of the whole group of IBD patients was 37.8 +/- 11.3 (range 16-76) years. Thirty-eight patients (3.3%; 26 with ulcerative colitis/12 with Crohn's disease, 21 males/17 females, aged 61.3 +/- 13.4, range 33-77 years), were diagnosed with 42 cancers. Cancers occurred 5.4 +/- 3.3 (range 0-11) years after inflammatory bowel disease diagnosis. Colorectal cancer was diagnosed in 8 (1 Crohn's disease and 7 ulcerative colitis patients - 0.3 and 0.9% of the Crohn's disease and ulcerative colitis cohort, respectively) of 38 patients and 30 cancers were extra-intestinal. Four of 38 patients (10.5%) were diagnosed as having 2 cancers and they were younger compared to patients with one cancer (p = 0.0008). There was a trend for a higher prevalence of intestinal cancer in the northern centers (0.9%) compared to southern centers (0.3%, p = NS). Southern centers had more cases of extra-intestinal cancer compared to northern centers (2 vs. 3.8%, p = 0.08). Ten patients (0.9%; 8 with ulcerative colitis/2 with Crohn's disease, 8 males, aged 62.3 +/- 14.1 years) had colorectal dysplasia. Conclusions: In the first decade of the EC-IBD Study Group cohort follow-up study, the prevalence of cancer was as expected with most patients having a single neoplasm and an extra-intestinal neoplasm. In northern centers there was a trend for more intestinal cancers, while in southern centers there was a trend for more extra-intestinal cancers compared to northern centers. Copyright (c) 2007 S. Karger AG, Basel.