OBJECTIVES: In acute sub-massive pulmonary embolism (PE), Low Molecular Weight Heparins (LMWH) are as effective as IV unfractionated heparin (UFH), but easier to administer with a slightly better adverse events profile. In order to assess the health economic consequences of LMWH, we examined the cost of using the LMWH tinzaparin instead of UFH in the treatment of acute sub-massive PE in Belgium, from a hospital perspective. METHODS: The evaluation is based on a clinical trial involving 612 patients (Simonneau et al, NEJM, 97), reporting differences in the adverse outcomes of both treatments. In order to represent actual clinical practice in Belgium, a 2-round Delphi-panel was conducted in which clinicians produced data about average treatment patterns. A patient record review looking at actual clinical treatment of 54 patients with PE in five Belgian hospitals was used to validate the findings from the panel. Initial treatment costs that differed between the two strategies and costs of adverse outcomes reported in the trial were considered, since other costs (e.g. diagnosis) are the same for both options. Drug costs were obtained from list prices, and staff costs and material costs were provided by University Hospital Gent. RESULTS: Even though treating PE with tinzaparin increases drug costs, the total cost of treating a patient is less than treatment with UFH: Bef 4,817 (119.4 Euro) for UFH vs. Bef 3,837 (95.1 Euro) for tinzaparin. Tinzaparin removes the need for aPTT tests, and produces savings on staff time, material usage, and treating adverse events. The results are robust both to the plausible range of uncertainty in the results of the clinical trial and to broad changes in the medical resource use data. CONCLUSIONS: Overall, tinzaparin reduces costs through greater ease of administration, saving staff time and material costs, and by removing the need for laboratory monitoring.