OBJECTIVES: The objective of this study was to collect information about health care resources used in the Intensive Care Unit (ICU) to treat pediatric patients with acute respiratory distress syndrome, and to calculate total treatment costs. To collect this information, the use of administrative databases or hospital records was considered. The latter method was used. Costs for each resource were estimated through micro and gross costing. METHODS: A non-comparative retrospective cohort study was conducted using hospital records. The study population was comprised of pediatric patients treated in the ICU of the Sainte-Justine Hospital. Selected were ninety-six (96) patients who required ventilation support following acute respiratory distress syndrome in 1996. All hospital files were reviewed to collect data on patient characteristics, diagnoses, hospitalizations, professional fees, medical interventions, medication use, laboratory tests, and complications. These data were collected from the first day the patients were admitted in the ICU, until the day they were transferred to another ward. A trauma physician, a pharmacist, and an inhalation therapist helped to develop the Clinical Research Form (CRF). Two research nurses completed the CRFs, and a clinical research assistant collected cost data. RESULTS: The use of micro costing is a very reliable way of estimating treatment costs. However, it was found to be a long and expensive process. In our study, research nurses spent up to 8 hours per record to collect the information needed to complete the CRF. CONCLUSION: Given the extensive time needed to realize micro costing studies, it is understandable that modelization has occupied a big place in pharmacoeconomic evaluations. However, in some cases, even modelization cannot replace micro costing. Alternative ways, such as the use of administrative databases, should be considered. However, in Quebec, there is still a need to assess the reliability of using administrative databases for economic evaluations.