Inflammatory bowel diseases (IBD), consisting of Crohn's disease (CD) and ulcerative colitis (UC), are chronic immune mediated diseases of unknown aetiology. Traditionally, the highest occurrence of both UC and CD is found in North America and Europe, including Scandinavia and the United Kingdom, while the diseases remain rare in Eastern Europe. Until recently, few population-based cohort data were available on the epidemiology of IBD in Eastern Europe. However, recent studies from Hungary and Croatia have reported steep increases in IBD incidence that means they are now comparable with Western European countries. The reasons for these changes remain unknown but could include an increasing awareness of the diseases, better access to diagnostic procedures, methodological bias in previous studies from Eastern Europe, or real differences in environmental factors, lifestyle and genetic susceptibility. The aim of this thesis was to create a prospective European population-based inception cohort of incident IBD patients in order to investigate whether an East-West gradient in the incidence of IBD exists in Europe. Furthermore, we investigated possible differences throughout Europe during the first year subsequent to diagnosis in terms of clinical presentation, disease outcome, treatment choices, frequency of environmental risk factors, as well as patient-reported health-related quality of life (HRQoL) and quality of care (QoC). Finally, we assessed resource utilization during the initial year of disease in both geographic regions. A total number of 31 centres from 14 Western and 8 Eastern European countries covering a total background population of approximately 10.1 million participated in this study. During the inclusion period from 1 January to 31 December 2010 a total number of 1,515 patients aged 15 years or older were included in the cohort. Annual incidence rates were twice as high in Western Europe (CD: 6.3/100,000; UC: 9.8/100,000) compared to Eastern Europe (CD: 3.3/100,000; UC: 4.6/100,000), thus confirming a gradient in IBD incidence. The incidence gradient could not be explained by marked differences in environmental factors prior to IBD diagnosis. In fact, Eastern European patients had higher frequencies of dietary risk factors than Western European patients, while the remaining risk factors occurred just as frequently. Furthermore, the availability of diagnostic tools and the diagnostic strategy did not differ, and in fact was better in Eastern Europe in terms of the use of colonoscopies and diagnostic delay. In terms of socio-economic characteristics as well as clinical presentation at diagnosis Eastern and Western European IBD patients did not differ significantly. However, regarding treatment choices during the initial year of disease the use of biological therapy was significantly higher in Western Europe for both CD and UC, while Eastern European centres used 5-ASA more often in CD and UC. In both regions patients were treated earlier and more frequently with immunomodulators compared to previous cohorts. But despite these differences in treatment, disease course - including hospitalisation and surgery rates during the first year of disease - were similar in both regions and the majority of patients were in clinical remission at follow-up. Finally, generic and disease-specific HRQoL improved in all IBD patients and at twelve months follow-up the majority of patients had a good disease-specific HRQoL score. Differences in how, and from whom, patients received disease-specific education and information were noted between the geographic regions; for instance IBD specialist nurses were not used in Eastern European IBD centres. Expenses for the cohort during the initial year of disease exceeded four million Euros with most money spent on diagnostics and surgery. Biological therapy accounted for one fourth costs in Western European CD patients. Long-term follow-up of the EpiCom cohort is needed in order to assess whether the earlier and more frequent treatment with immunomodulators and biologicals observed in this study will change the natural disease course and phenotypes over time or merely postpone outcomes such as surgery. Furthermore, the question of if and how differences in treatment choices between Eastern and Western Europe impact on the disease course requires long-term follow-up.