Acute renal failure (ARF) with loin pain after exercise with development of wedge-shaped contrast enhancement on computed tomography (CT) has been described as a new disease entity. We report 2 patients who developed ARF with severe loin pain after exercise, showing wedge-shaped lesions both on CT and ultrasonography. Renal ultrasonography showed indistinct wedge-shaped lesions when performed at oliguric or recovery phase of ARF, whereas it showed distinct lesions when done between these two phases. Contrast CT performed at the recovery phase disclosed distinct wedge-shaped lesions. Our findings suggested that the best time to detect these lesions by ultrasonography is between at the beginning of diuresis and at the time of serum creatinine levels of 2 mg/dl.