Knowledge about the total actual treatment cost of a patient is important in order to negotiate about a reimbursement system and for decision making purposes within the hospital and the ICU-unit. This project will focus on the treatment cost of a patient with cardiac surgery pathology within the ICU-unit of the University Hospital. Nowadays Activity Based Costing is promoted as the best allocation method, also in the context of hospitals. However in the presence of resources provided on a joint and indivisible basis (which is often the case in hospitals) this method does not produce relevant costs for decision making. ABC based on an assumed linear relation between costs and activities can yield poor approximations to actual expenditures, which play an important role in the determination of the reimbursement by the government and the insurers. Besides the problem of joint costs, there is the issue of case mix within the ICU. In this context the question arises whether the cost for a specific activity can be generalised over the different pathologies or whether the costs are unique per pathology. In the first phase of the project the total cost per patient will be calculatcd with the use of different cost allocation methods (conventional coating, ABC, costing based on joint and indivisible resources) for the pathology cardiac surgcry. In this way we want to study if ABC information provides reliable signals for decision making (e.g. the approximation to actual expenditures, the usefulness for cost savings in the hospita! context). In the second part of the project the effect of case mix on the cost per patient in an ICU will be studied through a comparison of the results of this study with the general results of the SAPI-study.