Inflammatory bowel disease (IBD) is a chronic condition of uncertain etiology that pro-duces inflammation of the alimentary canal, primarily the small intestine and the colon. Crohn’s disease (CD) and ulcerative colitis (UC) are its two main phenotypical mani-festations. The current hypothesis for its pathogenesis is that a combination, or combi-nations, of genetic and environmental factors alter regulation of the immune system. Epidemiological studies of patterns of geographic and demographic variation cons-titute invaluable tools for exploration of possible causes for the development of this disease as well as for identification of specific local risk factors that may influence its incidence, evolution and clinical behavior. This information can also be fundamental for making rational decisions about allocation of health care resources and for developing early detection and treatment programs in any community. Nevertheless, there are very large impediments in the way of conducting epidemiological studies of IBD: diagnosis is difficult and there is no gold standard for identifying this disease. Early symptoms are not very specific, and they can simulate many other diseases. Comparative epidemiolo-gical studies between populations constitute a great challenge due to the variability of clinical criteria used, and regional variations in availability of endoscopic procedures and the levels of knowledge among doctors. All of this can influence whether or not cases are detected, thus becoming a determining factor in the validity of reports. Many epidemiological studies have been performed based on diagnoses made upon hospita-ble admission. These statistics underestimate the true levels of incidence because a great proportion of patients nowadays are never hospitalized. All of the preceding serves to remind us that, when comparing epidemiological studies, differences between popula-tions can be due to the methodologies used and not to true environmental or genetic differences.On a global scale IBD annual incidence rates vary widely: from 0.5 to 24.5/100.000 inhabitants for UC, and from 0.1 to 16/100,000 inhabitants for CD. IBD prevalence has reached 396/100.000 (1,4). During the past few years the incidence pattern of both diseases has changed dramatically, especially their geographic distributions (1). Every day more studies add support to the finding that the predominance of UC incidence over CD incidence is diminishing over time. In many countries prevalences of CD are being observed that are greater than those reported in earlier studies (2). Traditionally the highest incidence rates for have been reported in North America and western Europe while the lowest rates have been reported in Eastern Europe, Africa, South America and Asia. These regions of the world traditionally constituted the so called zones of low risk (1,4). Recent studies have shown a change in tendencies from these traditional inci-