Deeply phenotyped IBD cohorts with a biobank are ideal tools for this type of research, and are warranted. Most IBD biobanks reflect hospital based populations thereby over representing severe and therapy refractory patients. However, many hypotheses require designs with a full IBD spectrum. Secondly, phenotypes are mostly ascertained retrospectively, which makes results prone for bias. As no prospective population based biobank excists, we started the population based IBD South Limburg (IBDSL) biobank project.