Since the introduction of diagnosis-related groups (DRGs) many surgical departments report inappropriate reimbursement for complex cases and a shift in costly cases. To evaluate this situation, the German Society for Visceral Surgery inaugurated the present cost calculation project. In three university hospitals for 50 cases each, we depicted possible cost separators and utilized the complete cost calculation data (so-called Paragraph 21 data set) to test these separators. We identified "admission from another hospital", "severe surgically relevant concomitant disease", and "reoperation during the same hospital admission". The last was considered the economically most significant and medically most valid factor and was submitted as a possible modification to the german DRG system. The proposed cost separator "reoperation during the same hospital admission" was introduced into the DRG system after validation and leads to better allocation of reimbursements to complex and costly cases.