OBJECTIVES: Previous research suggests heparin to prevent DVT following orthopaedic surgery is value for money. Recent trials indicate that extending the duration of prophylaxis may prevent additional DVT’s, but increase the cost of prophylaxis. The objective of this study was to compare the expected costs and benefits of using enoxaparin (a low molecular weight heparin) for the index hospital admission only versus enoxaparin for hospital admission and 21 days post discharge. METHODS: Decision analysis was used to combine probability, resource use and unit cost data, from the perspective of the UK NHS and patients. Expected costs and benefits of standard and extended regimes were estimated for a hypothetical cohort of 1000 patients undergoing elective hip replacement. Three alternative measures of outcome were used: lives gained, life years gained and quality adjusted life years (QALY) gained. Costs of events were estimated as quantity and type of health care resources used, multiplied by unit costs. Data for the model was based on point estimates from a review of clinical and economic literature. Statistical techniques were not appropriate to assess the level of uncertainty associated with the results. Sensitivity analysis across minimum and maximum values of variables was used to test the robustness of the results. RESULTS: The expected cost per QALY for extended enoxaparin was £3,145 (range £1268/QALY to £15212/QALY). Extended enoxaparin was cost saving if 66% of patients or carers could administer prophylaxis post discharge. CONCLUSIONS: Whilst conservative data were used to bias the analysis against extended enoxaparin, limitations in the data and modelling techniques mean that the results of the analysis are only indicative of the potential value for money. The results indicated extended enoxaparin was associated with a cost/QALY of £1268-£15212, which compares well with the cost/QALY for other health care interventions funded by the UK NHS.