Aspirin has been shown to be as effective (P <0.001) and safe as low-molecular-weight heparin (dalteparin) for the extended prevention of venous thromboembolism after total hip arthroplasty (THA). In this study, all patients initially received dalteparin for 10 days following surgery and were then randomized to receive either aspirin (n = 386) or dalteparin (n = 400) for a further 28 days. Thus, aspirin might be a convenient and inexpensive alternative to low-molecular-weight heparin for extended thromboprophylaxis post-THA.