Mycotic renal artery aneurysms are rare and can be difficult to diagnose. Classic symptoms such as hematuria, hypertension, or abdominal pain can be vague or nonexistent. We report a case of a 53-year-old woman with a history of intravenous drug abuse presenting with critical limb ischemia, in which CT angiography identified a mycotic renal aneurysm. This aneurysm tripled in size from 0.46 cm to 1.65 cm in a 3-week interval. Echocardiography demonstrated aortic valve vegetations leading to a diagnosis of culture-negative endocarditis. The patient underwent primary resection and repair of the aneurysm, aortic valve replacement, and left below-knee amputation after bilateral common iliac and left superficial femoral artery stenting. At 1-year follow-up, her serum creatinine is stable and repaired artery remains patent.