Multicenter, randomized, double-blind, placebo-controlled. A total of 253 patients were randomized to usual care plus placebo and a total of 255 patients to usual care plus a three-to-four year regimen of low-dose warfarin (target INR 1.5 to 2.0), which after initial titration required infrequent outpatient monitoring. Double-blind INR assessment and dose adjustment were performed every three months to ensure patient safety and to monitor compliance. Primary endpoints included recurrent venous thromboembolism, major bleeding episodes, and all-cause mortality. Separate analysis was performed of all-cause mortality in the total patient population and in those with factor V Leiden.