OBJECTIVE To report three patients, each of whom had acute rethrombosis of a reopened middle cerebral artery after urokinase treatment for proximal stenosis (percutaneous transluminal angioplasty of the stenosis was performed adjunctive to the thrombolytic treatment to preserve the success of the thrombolysis), and a fourth patient who had percutaneous transluminal angioplasty right after the completion of thrombolysis and had no rethrombosis despite a partial dilatation of the severe stenosis. METHODS Thrombolytic treatment was carried out by a coaxial technique with a Tracker 18 catheter through a 5-F angiographic catheter; 80,000 U in 5 mL of urokinase were intermittently injected every 15 minutes after an initial dose of 250,000 U. All patients were given 3000 U of heparin with a booster dose of 1000 U every hour. Angioplasty was performed with a Stealth catheter balloon, 2 to 3 mm x 1.5 cm. RESULTS Three patients recovered without hemorrhage after percutaneous transluminal angioplasty and thrombolytic treatment. Percutaneous transluminal angioplasty was unsuccessful in one patient because of the inability to pass a 2-mm Stealth balloon catheter, and the result was a second rethrombosis. This patient had a poor recovery. CONCLUSIONS Acute thrombosis of the middle cerebral artery may be associated with severe proximal stenosis. Rethrombosis may occur even after complete thrombolysis. Percutaneous transluminal angioplasty may be safely performed to prevent rethrombosis.