When urine drainage from the renal pelvis is blocked, the pressure in the kidney increases after accumulation, the renal pelvis and calyces dilate, the renal parenchyma atrophies, and the function decreases, which is called hydronephrosis. When the volume of hydronephrosis exceeds 1000 ml or the total amount of urine in a child exceeds 24 hours, it is called giant hydronephrosis. Clinical manifestations of hydronephrosis vary and mainly include pain in the renal region, nausea and vomiting, and urinary retention. Urinary tract obstruction is one of the main causes of hydronephrosis. Patients with acute upper urinary tract obstruction often present with nausea and vomiting, hematuria, and pressure pain in the renal region. Some patients with upper urinary tract obstruction have insignificant symptoms or only vague pain and discomfort in the lower back. When it develops into huge hydronephrosis, a mass may appear in the abdomen. Patients with hydronephrosis should go to the hospital in time and be treated under the guidance of specialized physicians.