The ages of patients with Crohn's disease (CD) and ulcerative colitis (UC) are characterized by a bimodal distribution. The present study used hospital statistics to compare the age distribution of inflammatory bowel disease (IBD) among different countries.: Hospital statistics from the period 1994 to 2007 were obtained through special requests to the national statistical offices of 9 European countries. Hospitalization was expressed as age- and sex-specific rates per 10,000 living people.Hospitalization rates of different countries varied between 1.2 and 4.3 discharges per 10,000 for CD and between 0.7 and 4.7 discharges per 10,000 for UC. Countries with high CD rates were associated with similarly high UC rates (r = 0.955, P < 0.0001). In all countries alike, the age-distribution of CD hospitalization was characterized by a large peak in younger patients followed by a small peak in older patients. UC hospitalization was characterized by a small peak in younger patients followed by a large peak in older patients.The bimodal age distribution of IBD hospitalization can be explained in terms of varying exposure to 2 separate environmental risk factors that affected consecutive age groups differently over the course of the 20th century.