Epidemiological studies of inflammatory bowel disease are important in order to find possible clues to the still unknown etiology, as well as for the planning of the health service. In supplement to short-term studies, reporting the actual state of the disease, long-term studies are requisited to follow up the development of inflammatory bowel disease. Inflammatory bowel disease has become more frequent during the past decades, with an approximate prevalence of 0.5% in the northern part of the world. A changed disease panorama can be noted with increasing median age at diagnosis, a growing entity of patients with colorectal Crohn's disease and a shift towards more distal ulcerative colitis. The increased age at diagnosis is attributed to a postponement of the age-specific incidence peak. While the difference between gender has levelled off, difference still exists in young adults in Crohn's disease and in elderly in ulcerative colitis. Colorectal cancer has become a matter also in Crohn's disease.