BACKGROUND Hip fracture surgery (HFS) carries a high risk of venous thromboembolism (VTE) in the absence of thromboprophylactic treatment. Previous reports have suggested that fondaparinux sodium (FPX) administration decreases the incidence of VTE after HFS and total hip and knee arthroplasties. However, investigations of that effect in Japanese populations remain inadequate. We evaluated the efficacy of FPX after HFS in a prospective randomized controlled trial. METHODS Subjects comprised 76 consecutive Japanese patients who underwent HFS and were randomly assigned to the FPX group, who received subcutaneous injections of FPX 2.5 mg/day for 14 days beginning the next after HFS, or the control group (non-FPX group). D-dimer values were measured on admission and 7 and 14 days after HFS. Subjects with D-dimer levels over the cutoff value (> 20 microg/ml on day 7) underwent enhanced computed tomography (CT) to evaluate the possibility of deep vein thrombosis (DVT) of the lower extremities. D-dimer values, the incidence of DVT, and side effects associated with a bleeding tendency (i.e., hematoma or massive bleeding) were compared between groups. RESULTS The FPX group showed significantly lower D-dimer levels than the non-FPX group at 7 and 14 days after HFS (P < 0.05). Only one case in the FPX group exceeded the D-dimer cutoff compared to 12 cases in the non-FPX group (P = 0.001). DVTs were found with enhanced CT in one case in the FPX group and in five cases in the non-FPX group. In the FPX group, symptomatic hematoma at the surgical site and/or decreased hemoglobin > 2 g/dl was noted in four cases (10.5%). Postoperative drainage volumes did not differ significantly between groups. CONCLUSIONS FPX administration demonstrated positive effects on the prevention of VTE after HFS. However, careful postoperative observation is warranted to prevent serious side effects after FPX administration.