Background: Since 2004 surgical procedures done in German hospitals have been paid for by a flat-rate reimbursement scheme based on diagnosis-related groups (DRGs). The aim of the present detailed cost analysis study was to identify the major factors that determine the costs of intensive care medicine. Methods: In a patient-based investigation lasting 6 months, 104 patients (mean age 64.6 years) on an interdisciplinary surgical intensive care unit were analyzed over 309 hospital occupancy days. Demographic data, drugs administered, infusions, nutrition, blood and coagulation products, invasive measures and monitoring, artificial respiration parameters, other measures and diagnostic services (laboratory, microbiology, x-ray, etc.), as well as four intensive scores (SAPS II, APACHE II, SOFA, TISS 28) were recorded daily. Results: The overall cost of 309 occupancy days (n=104) amounted to 457,564.11 euros, the average cost per day being 1,480.78 euros, and the mean case-specific cost 4,7.47.48 euros. 49 % of the overall cost was generated by medical staff, with medication and material each accounting for 18 %. Of the personnel costs, 70 % were caused by the nursing staff, 22 % by the medical staff and 8 % by cleaning and other personnel. During the course of hospitalisation, an non-significant increase in the costs generated by personnel was observed. A linear correlation was found between cumulated TISS 28 and the mean case costs. While there was no significant relationship between patient-specific score levels and individual case cost, the correlation between length of stay (LOS) and case cost was highly significant. Conclusions: The determining factor in the cost calculation of intensive care medicine are personnel costs. Overall cost is determined largely by the LOS, with such additional factors as age, diagnosis, comorbidity, etc. playing only an insignificant role.