Prophylactic anticoagulation with sodium warfarin was used after 1,950 of 2,012 consecutive total hip arthroplasties, beginning on the fifth postoperative day. No anticoagulative was used after the remaining procedures. The rate of fatal pulmonary embolism in the group treated with anticoagulants was 0.05 per cent, and in the group not treated with anticoagulants, 3.4 per cent. There were nineteen serious bleeding problems in the anticoagulated group, six of which necessitated surgery. There were also two deep infections associated with wound hematomas which resolved satisfactorily with treatment. There were no fatal complications resulting from anticoagulation.