BACKGROUND AND AIMS: Inflammatory Bowel Disease (which includes Crohn's Disease and Ulcerative Colitis), is a chronic condition characterised by substantial morbidity. Inflammatory Bowel Disease patients are considered expensive to manage, hence accurate estimates of care costs are crucial to help healthcare providers plan clinical management. The aim of this study is to estimate the cost of care for Crohn's Disease and Ulcerative Colitis patients in the United Kingdom and Western mainland Europe. METHODS: Decision models were built to simulate thenatural disease history of Crohn's Disease and Ulcerative Colitis, informed by United Kingdom and European clinical pathways. A healthcare provider perspectivewas adopted, model inputs were informed by published sources and expert opinion,and UK healthcare costs were used (2008 prices). Cohorts of 25 year old patientspresenting with symptoms of varying severity were modelled over ten years, and annual treatment costs calculated per patient. RESULTS: The average annual cost of care per Crohn's Disease/Ulcerative Colitis patient was pound631/ pound762 (United Kingdom) and pound838/ pound796 (Europe). Most costs were incurred immediately following diagnosis, particularly in European Crohn's patients, reflecting the earlier use of more aggressive treatments. Surgery, hospitalisation, and the use of biological therapies and mesalazine (in Ulcerative Colitis) were key cost drivers. The total annual cost to the United Kingdom National Health Service of caring for Inflammatory Bowel Disease patients was estimated to be pound131million. CONCLUSIONS: This study confirms that Inflammatory Bowel Disease patients are expensive to manage and illustrates the importance of differentiating between alternative clinical management scenarios.