A rare case is presented of mechanical ileus caused by a giant cystic kidney. With absent symptoms from the urinary tract, the patient was operated on in emergency situation, and the diagnosis of polycystic renal degeneration in a 64-year-old female patient was made during the operation. The fact is worth stressing of sure imposition in the X-ray image of the signs of ileus and of presence of fluid within numerous renal cysts, and in case of lacking other signs this may lead to diagnostic errors.