Abstract Background and Aim: Because of its long duration, inflammatory bowel disease (IBD) causes high use of health services and high lifetime costs for medical care. The aim of the present study was to measure the costs of outpatient care in patients with IBD in a German University Hospital and to identify potentially relevant determinants of costs. Methods: The use of resources of 599 outpatient patients treated at a German University Hospital (65% Crohn's disease [CD] and 26% ulcerative colitis [UC]) was measured using a routine database. Costs of medical services (diagnostics and treatment) were considered as well as costs of medication. Resource use was valued using fee schedules for hospital services and pharmacy prices for drugs. Results: The mean cost of one outpatient visit was €162, including physician costs, laboratory costs, and costs of diagnostic procedures following the visit. For a subgroup of 272 patients, the mean annual cost for outpatient care was €3171. Medication accounted for 85% of the total annual costs. Potential determinants, such as main diagnosis (CD or UC), sex, age, localization of disease, and occurrence of anemia, had no influence on costs, whereas complications of IBD and use of corticosteroids showed an impact on annual costs. Conclusions: This is the first time that the structure and range of outpatient treatment costs for IBD have been demonstrated for a German hospital.