Giant hydronephrosis is rare and usually presents during childhood as a unilateral renal mass due to congenital anomalies such as pelvi-ureteral junction obstruction. In adulthood, however, other etiologies such as urolithiasis may supervene. We report on a 75-year-old female patient who presented with right-sided abdominal pain. She had a visible right renal mass with smooth surface and cystic consistency. Urine analysis showed 60–80 pus cells/HPF and serum creatinine level was 1.2 mg/dL. Imaging revealed hugely dilated kidneys with right severe hydronephrosis and lost renal parenchyma due to a large middle ureteral stone. The left kidney had variable parenchymal thickness which was better at the lower pole with multiple stones. After counselling of the patient, simultaneous left pyelolithotomy with placement of a left JJ stent and right nephrostomy tube were done. Then, renal isotope scanning revealed diminished total glomerular filtration rate (54.6 mL/min/1.73 m2) with better left split function (61.2 vs. 38.8%). Accordingly, a right ureterolithotomy was done and the patient was followed up for 1 year with variable serum creatinine level between 1.2 and 1.5 mg/dL.