OBJECTIVE: To determine the cost effectiveness of extended prophylaxis with fondaparinux to prevent venous thromboembolism in patients undergoing hip fracture surgery compared to short term using UK and Dutch estimates of costs. METHODS: Costs and effects are modeled using a cohort simulation model. Short term transition probabilities (until day 30) are obtained from placebo controlled trials. Long term probabilities are obtained from the literature. UK resource use and costs were obtained from a published analysis concerning short term prophylaxis. Dutch resource use and costs were estimated in a separate costing study concerning bleedings and symptomatic events. Outcome measures were rates of symptomatic thromboembolic events, deaths avoided and health care costs. Costs were in 2004 values. “Confidence intervals” (CI) were obtained by probabilistic sensitivity analysis. RESULTS: At one year extending prophylaxis with fondaparinux after major orthopaedic surgery from 7 to 22 days was estimated to prevent 343 symptomatic venous thromboembolic events (per 10,000 patients) (95% CI:283-391). The additional cost (per patient) of extending the prophylactic period are estimated at £164 (£117-£212) in the UK and at € 66 in the Netherlands. The number of deaths avoided (per 10,000 patients) are estimated at 138 (89-192). Costs per symptomatic VTE avoided are estimated at £4,788 (£3,258-£6,906) in the UK and at €1,915 (€392-€4,021) in the Netherlands. Costs per death avoided are estimated at £11,932 (£7,220-£20,480) and €4,773 (€892-€11,629). When assuming the average survival after surgery at 6 years, costs per life year gained are estimated at under £3,000 for the UK and at under €900 for the Netherlands. CONCLUSION: Our estimates indicate that extending the prophylaxis with fondaparinux from 7 to 21 days has an acceptable balance between cost and outcomes both in the UK and The Netherlands.