Recent studies have demonstrated an increased incidence in the diagnosis of malignancy subsequent to the diagnosis of deep venous thrombosis or pulmonary embolus. We reviewed 237 patients with venographically proven deep venous thrombosis over eight years. Of these, 216 had at least one predisposing cause for deep venous thrombosis; of the remaining 21 patients, three had hemoglobin determinations revealing anemia and were subsequently shown to have a malignant disease. One patient had two chief complaints and was shown to have deep venous thrombosis and malignant disease. The 17 remaining patients underwent computed tomographic scan of the abdomen and seven (41%) had abnormalities which proved to be malignant in origin. One further patient was diagnosed with carcinoma of the cervix two months following the onset of deep venous thrombosis. The remaining 10 patients continued free of malignant disease. Five have died of circulatory causes in the follow-up period. Seven of the nine patients diagnosed with malignancy succumbed within six months of the diagnosis. We conclude that only a small group of patients with deep venous thrombosis will have no identifiable cause for deep venous thrombosis and be asymptomatic for malignancy. Complete blood count, physical examination and computed tomographic scan of the abdomen at the time of venographic diagnosis of deep venous thrombosis is useful in diagnosis of "occult" malignancy. The number of gynecologic tumors would suggest the need for pelvic examination as well as radiographic examination. The presence of deep venous thrombosis and malignant disease is an ominous prognostic sign.