The incidence and prevalence of inflammatory bowel disease (IBD) have distinctly changed over the past decades throughout Europe. From former North-South and West-East risk gradients, nowadays, classic high-risk areas for IBD in North and West present more stable incidences whereas in formerly low-risk zones the incidence is rising. These changes cannot be explained by genetic modifications in IBD patients' background, which draws attention to the possible existence of potent environmental factors triggering this epidemiologic shift. Important lessons can be drawn from different European population-based studies assessing the influence of environmental factors in familial IBD that may impact on the outcome of the disease and the management of the patients and their relatives.
Keywords: environmental factors; epidemiology; familial aggregation; inflammatory bowel disease.