Editorial on the Age Distribution of IBD Hospitalization T he inflammatory bowel diseases (IBD), consisting of Crohn's disease and ulcerative colitis, are chronic inflammatory conditions of the gut believed to occur in genetically predisposed individuals who are exposed to unknown environmental triggers. Despite numerous studies, only a few environmental risk factors have been consistently reproduced; however, they have not completely explained the processes that drive IBD. 1 One interesting epidemiological phenomenon is a bimodal distribution of age at diagnosis, whereby a peak in the incidence of disease is observed in the second and third decades of life, followed by a second rise in the elderly. 1,2 The presence of bimodal peaks suggests a complex interaction between genes and environmental exposures. Possibly, genes play a more important role in the young and environmental exposures in the elderly; alternatively, environmental factors may differentially affect individuals by age. Although several studies have reported a bimodal age distribution for IBD, [3][4][5][6][7] others have not supported this finding. [8][9][10][11][12][13] In this issue of Inflammatory Bowel Disease, an article evaluates the distribution of age at onset of Crohn's disease and ulcerative colitis in European countries. Sonnenberg used administrative databases to identify discharge abstracts of patients with International Classification of Diseases 9th (ICD-9) or 10th (ICD-10) hospitalization codes for Crohn's disease or ulcerative colitis in Denmark, England, Germany, Italy, the Netherlands, Scotland, Spain, Sweden, and Switzerland. The hospital rates for the primary discharge diagnosis of IBD were age-and sex-stratified within each country. Sonnenberg illustrated a bimodal peak in the hospitalization of ulcerative colitis, with many countries demonstrating the highest hospitalization rates in elderly ulcerative colitis patients. In contrast, hospitalization rates for Crohn's disease were consistently highest in young adults, with either a smaller or flat peak in the elderly. The author concluded that this multicountry assessment supports the argument for a bimodal age peak and that this finding, as well as others, 3-7 supports the notion that environmental influences differentially affect the pathogenesis of Crohn's disease and ulcerative colitis. However, the data should be interpreted in the context of the limitations of studying IBD with administrative databases.