A 42-year-old man with a high-grade left internal carotid artery (ICA) stenosis demonstrated on a duplex scan was referred to us. A cerebral arteriogram confirmed a greater than 90% left internal carotid stenosis, but with the unexpected finding of a moderate amount of thrombus in the proximal ICA. He underwent emergent left carotid endarterectomy, but during the operation, only a small amount of thrombus was identified as adherent to the atherosclerotic plaque. he awakened in the operating room with a dense right hemiplegia and aphasia. Immediate reexploration demonstrated a patent endarterectomy site, a distal thromboembolectomy was performed without extraction of thrombus, and urokinase (250,000 Units) was infused into the distal ICA. He reawakened with an unchanged right hemiplegia and aphasia. The patient then underwent an urgent postoperative carotid and cerebral arteriogram that demonstrated an embolus to the middle cerebral artery. he was treated with the superselective infusion of urokinase (500,000 Units), with almost complete resolution of the clot. Over the course of the next 48 hours, the patient made a nearly complete neurologic recovery, and he was discharged from the hospital with only a slight facial droop. At 2 months' follow-up he was completely neurologically healthy. To our knowledge this is the first reported case of urokinase administered in the immediate postoperative period in the angiography suite to treat a thromboembolus complicating a carotid endarterectomy.