We report a case in which a renal scan and angiography revealed a renal artery thrombosis. The only presenting symptom was left flank pain and no predisposing factors could be found on clinical or laboratory examination. Local infusion of streptokinase through an intra-arterial catheter led to complete dissolution of the thrombus despite the fact that it had been present for 13 days. The renal scan immediately after thrombolysis demonstrated the dramatic return of function to the involved kidney, although a repeat scan at 3 months showed evidence of the previous ischemia. Selective fibrinolytic therapy offers an option to surgery in selected patients with renal artery thrombosis.