The aim of the study was to determine whether the total cost estimate of a hospital service remains reliable when the cost components of bottom-up microcosting were replaced by the cost components of top-down microcosting or gross costing. Total cost estimates were determined in representative general hospitals in the Netherlands for appendectomy, normal delivery, stroke and acute myocardial infarction for 2005. It was concluded that restricting the use of bottom-up microcosting to those cost components that have a great impact on the total costs (i.e., labour and inpatient stay) would likely result in reliable cost estimates.