Fondaparinux efficacy for thromboprophylaxis was evaluated in predefined high-risk hip fracture patients. Patients received fondaparinux 2.5 mg for 7 days following surgery; 656 patients were randomized double blind to receive placebo or continue fondaparinux regimen for 21 additional days. Primary efficacy was venous thromboembolism (VTE) based on bilateral venography during the double-blind period. Total VTE was 1.4% (3 of 208 patients) for extended prophylaxis and 35% (77 of 220 patients) for short-term prophylaxis (P = 0.001), relative risk reduction (RRR) of 96%. Major bleeding occurred in 2% (8 of 327 patients) with extended prophylaxis and in 0.6% (2 of 329 patients) with short-term prophylaxis (P =.063). Risk of VTE was continued following short course fondaparinux in hip fracture patients, but was significantly reduced by extending prophylaxis, without significant risk of major bleeding.