During a five year period at Akron City Hospital, 165 Greenfield filters were placed in 165 patients. Of this group, 78 patients were available for long term analysis, and of these, 42 did not receive anticoagulation treatment for venous thromboembolic diseases, either acutely or on an outpatient basis. An analysis of the outcome for these 42 patients who had the Greenfield filter only as the primary mode of therapy for the disease included chart review and asking each person a standard set of questions. Leg swelling was the most common complaint, occurring in 33 per cent of patients. Venous stasis ulceration occurred in two patients and recurrent deep venous thrombosis occurred in one patient. When compared with a historical control group with venous thromboembolic disease that was treated with anticoagulation alone, the incidence of these sequelae in Greenfield-treated patients was not significantly different. Finally, in this review, the Greenfield filter is better than 95 per cent effective in the prevention of pulmonary embolism. This is no less effective than anticoagulation alone, the efficacy of which is 95 to 98 per cent. The placement of a Greenfield filter is a safe procedure that can usually be done after a local anesthetic was administered to the patient with a complication rate of less than 10 per cent. Unfortunately, major complications of anticoagulation (usually hemorrhage) are relatively common at a rate of 2 to 15 per cent, and occur more frequently in the older population. It is for reasons of safety of therapy and of an equal or better efficacy that the Greenfield filter is recommended in a broader range of clinical circumstances. In particular, it is concluded that the Greenfield filter should be used as a primary means of therapy in venous thromboembolic disease, particularly in those patients who are more than 65 years of age, when the risks of anticoagulation are most threatening.