Two patients with spontaneous retrocarpal radial artery thrombosis are reported. Both patients had numbness and cold intolerance of the thumb and index finger and one patient had splinter hemorrhages. Angiography revealed identical occlusions of the radial artery over a 2.5 cm segment dorsal to the wrist. Both patients had complete palmar arches. Flow from the ulnar artery was sufficient to prevent frank necrosis of the thumb but not to prevent ischemic symptoms. Both patients were successfully treated by resection of the area of thrombosis and interpositional vein grafting by use of microsurgical techniques. Symptoms resolved after operation in both cases. Follow-up examinations 3 months and 5 1/2 years later revealed continued graft patency.