A recently published statistical summary of the occurrence of fatal pulmonary embolism among surgical cases that have come to necropsy in a large American clinic during the last ten years shows an incidence of 6 per cent.1 This is a figure of sufficient magnitude to warrant critical study. It might be expected that the formation of thrombi or other emboli is dependent primarily on the surgical interventions that have occurred in the recorded fatalities. Injuries to the walls of blood vessels with resultant thrombosis are an inevitable accompaniment of many operations. Indeed, as a surgeon has remarked, thrombosis within veins that have been cut is a normal occurrence and necessary to the completion of any surgical procedure. This should extend within the vessel to the point of entrance of the next tributary vein; when it extends beyond this point into the larger vessels, a pathologic condition of grave peril is created, as portions of the clot may become detached in the blood stream. The new study indicates, however, that frequently the site of operation is not of paramount importance in determining the site of thrombosis and the source of emboli. According to Henderson's1 observations at the Mayo Clinic, patients who die from pulmonary embolism are older than the average surgical patient; they are somewhat overweight, and, as a group, have a normal or somewhat subnormal blood pressure; a high percentage have postoperative infections. While the importance of the operative procedure in determining the site of thrombus formation and the occurrence of pulmonary embolism cannot be overlooked, he adds, other factors, such as age, weight, general condition of the patient, efficiency of the circulation, bodily inactivity incident to almost any operative procedure and infection, should also be emphasized.