The giant hydroureteronephrosis is a rare condition. We report a case of a unilateral giant hydroureteronephrosis in an adult patient presenting as palpable abdominal mass secondary to ureterovesical junction (UPJ) stricture. A 51-year-old man presented with a 2-year history of a palpable abdominal mass. Physical examination revealed a grossly distended abdomen that the upper margin of distension was at the level of the epigastrium and the lower one at the suprapubic region. Abdominal ultrasound and computerized tomography demonstrated a very large cystic mass in the right side of retroperitoneum involving all the space from superiorly right sub-diaphragmatic area to the bladder inferiorly. The patient underwent exploration and a right giant hydroureteronephrosis as involving all the retroperitoneal space crossing midline to the left with a liquid content of approximately 7 l caused by stricture at the ureterovesical junction was seen. The hydronephrotic sac was thin and right nephroureterectomy was performed by opening the sac and draining-off the liquid. The literature was reviewed and the management of giant hydronephrosis was discussed.