Fondaparinux, a selective inhibitor of factor Xa, is the first of a new class of antithrombotic compounds, the synthetic pentasaccharides. Its benefit-to-risk ratio in preventing venous thromboembolism after major orthopedic surgery was investigated in four randomized, double-blind international phase III trials in patients undergoing surgery for hip fracture, elective hip replacement, and major knee surgery. Compared to enoxaparin, fondaparinux administered at a subcutaneous dose of 2.5 mg qd, starting postoperatively, reduced the overall incidence of venous thromboembolism up to day 11 by 55.2% (p < 0.001). The incidence of clinically relevant bleeding was low and did not differ between the two groups. Overall, fondaparinux achieved optimal efficacy and safety when treatment was initiated ≥ 6 h after the surgical procedure. In a further randomized double-blind trial, 4 weeks of prophylaxis with fondaparinux after hip fracture surgery reduced the risk of venous thromboembolism by 96% as compared to 1 week of prophylaxis, and was well tolerated. Fondaparinux has been recently approved for use in thromboprophylaxis after major orthopedic surgery. The clinical development of fondaparinux in other thromboprophylactic indications is ongoing.