In most reviews of arterial embolism or thrombosis the source of emboli or the cause of thrombosis can reasonably be established in over 90% of patients. Still about 10% remain without demonstrable cardiac or intraarterial sources. Although hypercoagulability induced by malignancy has been alluded to as a cause of unexplained intravascular thrombosis reports of arterial thromboembolism with such association are rare. Seven patients with unequivocal thromboembolism are presented. Two distinct clinical patterns are observed, one with in situ thrombosis of small arteries and the other with occlusion of large arteries causing limb ischemia or fatal organ infarction. The various pathogenetic mechanisms of arterial thrombosis or embolism in malignancy include sustained spasm of arteries, precipitation of cryoglobulins or other abnormal proteins in small arteries, direct tumor invasion of arteries, fragmentation and embolization of intracardiac or intraarterial metastases and spontaneous arterial thrombosis due to hypercoagulability. The hypercoagulable state can be recognized by the observation of shortened bleeding and clotting times, partial thromboplastin and prothrombin times, elevation of coagulation factors, platelets and yield stress index and resistance to anticoagulation. Patients presenting with arterial thromboembolic events with out demonstrable source should be investigated for malignancy. Conversely patients with malignancy should be searched for evidence of hypercoagulability in an attempt to prevent arterial thromboembolic complications.