A 57-year-old woman with an extensive cardiac history presented complaining of left flank pain. An intravenous pyelogram performed for the presumptive diagnosis of renal calculus showed poor function of the left kidney. Angiography demonstrated a 95% obstructing embolus in the left renal artery, which was removed surgically. This case illustrates some of the pitfalls in the diagnosis of renal artery obstruction and the need for a high index of suspicion. The intrarenal infusion of thrombolytic agents such as streptokinase may become the treatment of choice despite the success of surgical embolectomy. The diagnosis, laboratory analysis, and treatment of renal artery obstruction is discussed.