Clinical and radiologic diagnosis of a renal cortical abscess is difficult. A plain x-ray of the kidneys, ureters and bladder, an excretory urogram with nephrotomography, nephrosonography and renal angiography may not be helpful in the diagnosis. A case is presented of bilateral polycystic kidneys with a renal cortical abscess of the lower pole of the left kidney. An abscess could not be localized by the routine radiologic procedures. Gallium-67 scintigraphy demonstrated a renal cortical abscess of the left kidney, which was treated successfully by operation.