The primary objective of this study was to estimate the actual daily costs of intensive care unit stay using a microcosting methodology. As a secondary objective, the degree of association between daily intensive care unit costs and some patient characteristics was examined. This multicenter, retrospective cost analysis was conducted in the medical-surgical adult intensive care units of 1 university and 2 general hospitals in the Netherlands for 2006, from a hospital perspective. A total of 576 adult patients were included, consuming a total of 2868 nursing days. The mean total costs per intensive care unit day were 1911, with labour (33%) and indirect costs (33%) as the most important cost drivers. An ordinary least squares analysis including age, Nine Equivalent of Nursing Manpower Use score/Therapeutic Intervention Scoring System score, mechanical ventilation, blood products, and renal replacement therapy was able to predict 50% of the daily intensive care unit costs.