Thrombophlebitis of the superficial veins (SVT) of the leg is usually regarded as a mild and uncomplicated disease. Although this is generally true for acute thrombosis of the branches of the saphenous vein, the natural history of SVT involving the main trunk may not be as benign. The association of SVT with deep venous thrombosis (DVT) has been reported to range from 17 to 40%; the progression of the thrombotic process from the greater saphenous vein into the deep venous system has been reported in 8.6% of the cases. For this reason, even if symptoms of DVT are lacking, it is necessary to use duplex ultrasonography to be certain that DVT does not exist concurrently with SVT. In a recent study we found that saphenous-vein thrombi embolize even when no femoral-vein involvement is evident. Of 21 patients included in the study, findings compatible with a high probability of pulmonary embolism were detected in 7 (33.3%, 95% CI, 14.6 to 57.0), although clinical symptoms were present only in 1. The risk of pulmonary embolism is similarly high in patients with and without thrombosis at the sapheno-femoral junction. These patients presumably would benefit from anticoagulation, but such a benefit remains to be proven. Superficial thrombophlebitis, in the absence of DVT proven by duplex ultrasonography, is generally treated with nonsteroidal anti-inflammatory agents. A prospective randomized study is being carried out at our Institution evaluating therapeutic doses of anticoagulant drugs in SVT. Interim report suggests that, in thrombophlebitis of the thigh, high fixed doses of unfractioned heparin are more effective than low doses for the prevention of early and late venous thromboembolic complications and are not associated with an appreciable bleeding risk.