Greenfield filter as primary therapy for deep venous thrombosis and/or pulmonary embolism in patients with cancer. In 1985, as a result of the high complication rate associated with anticoagulants in patients who have cancer and deep venous thrombosis (DVT) and/or pulmonary embolism (PE), we established a policy of placing Greenfield filters (GFs) as primary therapy instead of anticoagulation. Since 1985 we have been asked to consult in the treatment of 18 patients with cancer and with DVT and/or PE, and we have placed a GF in each of these patients. This represented 34% (18/53) of the filters placed during that same period. Over the same 4-year period, 11 patients with cancer and DVT and/or PE underwent anticoagulation therapy. The purpose of this study was to compare the results of anticoagulation versus GF insertion in these two groups of patients. A significantly higher number of major complications (n = 4) occurred in the anticoagulation group (p less than 0.05, Fisher's exact test) than in the GF group (n = 0). The four complications that occurred in the anticoagulation group included three bleeding episodes (tumor bleeding, gastrointestinal bleeding, and hip hematoma) and one PE, despite adequate anticoagulation. Two patients died as a direct result of these complications (PE and gastrointestinal bleeding). The three patients with bleeding complications each required a transfusion of more than 3 units of blood. All four of the patients with complications had metastatic disease (pancreatic carcinoma, chronic lymphocytic leukemia, prostate carcinoma, and uterine carcinoma). Although this is a small, nonrandomized, nonprospective study, the data seem to indicate that GF placement is safer than anticoagulation for DVT or PE in patients with cancer and particularly in patients with metastatic disease. We conclude that GF insertions may be a better primary treatment than anticoagulation. 