Despite the apparent continuous increase of the incidence of inflammatory bowel disease (IBD) in some populations, or some sections of populations such as British children, the origin of these conditions remains obscure. Epidemiological studies of specific risk factors continue to yield contradictory and inconclusive results. However, studies of exposure and comorbidity, coupled with genetic and molecular studies, expand our knowledge and will facilitate more sophisticated research in the near future. Our understanding of the genetic basis of IBD is improving, but genetic anticipation as an explanation for increasing incidence rates appears less probable. The benefit of giving up smoking has been demonstrated in Crohn's disease patients, because smoking influences disease activity. The increased cancer risk in IBD is a concern, but despite this, the overall mortality in IBD is no higher than that of the general population.