For the past three and a half years postoperative venous thrombosis has been treated at the Lahey Clinic largely by anticoagulation therapy. For the last two and a half years femoral section and ligation have been reserved for cases of ambulatory recurrent calf phlebothrombosis with one or more benign pulmonary emboli or postoperative cases in which a second stage operation must be carried out. So far there have been one death from pulmonary embolism and four recurrent benign pulmonary emboli in 125 cases so treated. This death occurred early in the series after anticoagulation therapy had been needlessly abandoned to treat anemia with a transfusion. Three of the four recurrent benign pulmonary emboli recurred when the prothrombin time was not adequately reduced owing to insufficient dosage of Dicumarol (3,3'-methylene-bis-[4-hydroxycoumarin] ). In 2 of these cases Dicumarol therapy was continued, with subsequent adequate control of the prothrombin time and no further incident.