Twenty-eight consecutive cases of acute superficial thrombophlebitis of the long saphenous vein above the knee were reviewed concerning presence of asymptomatic deep venous thrombosis and pulmonary embolism and early clinical results after surgical treatment. Contrast phlebography of the ipsilateral leg revealed asymptomatic involvement of major deep veins of the thigh or calf in 4 of 21 examined patients. Perfusion lung scanning and chest radiography demonstrated typical segmental perfusion defects consistent with pulmonary embolism in two of ten examined patients. High ligation and stripping of the phlebitic veins gave prompt cure in 19 patients, though in two who were simultaneously treated with anticoagulants there was troublesome bleeding. Simple high ligation was performed in nine patients without complications, but four of them had protracted phlebitic pain. The results indicated that preoperative phlebography and lung scanning are helpful in detecting associated asymptomatic disorders and for planning therapy in patients with clinically isolated, superficial thrombophlebitis of the long saphenous vein. The treatment of choice is acute high ligation with removal of all phlebitic veins. If anticoagulation is indicated because of concomitant deep venous thrombosis or pulmonary embolism, the initial procedure should preferably be limited to high ligation.