How should the costs involved in clinical activities be calculated? The authors argue that interest for this question will increase in the years ahead. Costing requires several choices to be made both regarding principles and practical methodology. The results for high-cost treatments at the National Hospital in Norway (Rikshospitalet) are presented. The various treatments include bone marrow, liver, kidney, kidney-pancreas, heart and heart-lung transplantations, arterio-coronary bypass, valvular and aortic surgery, extra-corporal membrane oxygenation and surgical treatment of epilepsy. Methodological issues are presented and discussed. The costing is performed from an institutional perspective. Increased use of bottom-up, actual cost methodology, combined with the direct allocation of overheadcosts is recommended. This allows the study of interpatient variations in consumption of resources.