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Summary: Venous duplex scanning (VDS) is sensitive and specific for proximal deep-vein thrombosis (DVT) but has poor sensitivity for isolated calf DVT, some of which can extend to the proximal veins and result in clin-ically significant pulmonary emboli. The intent of this study was to determine the long-term outcome of outpa-tients with negative VDS and to assess the accuracy of three biochemical markers of hypercoagulability for the detection of DVT. Consecutive ambulatory patients re-ferred to our vascular laboratory with a question of lower extremity DVT had plasma determination of D-dimer, prothrombin fragment 1.2, and thrombin-antithrombin complex. Additionally, patients with a negative VDS were followed for 6 months to determine the frequency of subsequent venous thrombosis. Of 207 patients seen i