Upper urinary tract obstruction or ureteropelvic junction (UPJ) obstruction implies a functional impairment of urine passage from the pelvis to the ureter. UPJ is the most common congenital anomaly of the ureter. The incidence is two to three times higher in boys than in girls and mainly affects the left kidney. The widespread use of ultrasonography during pregnancy has increased antenatal hydronephrosis detection rates. The anteroposterior diameter of the renal pelvis, caliceal dilation, kidney size, parenchymal thickness, cortical echogenicity, ureters, bladder walls, and residual urine should be evaluated during ultrasonography. The first postnatal ultrasonographic examination should be performed from the 3–4th day of life due to physiological oliguria during the first days of life. Diuretic renography is an essential diagnostic tool, used for identifying renal pelvicalyceal dilatation with obstruction and a significant flow impairment requiring treatment. Interventional treatment should be provided if symptoms such as flank pain, pyelonephritis or stone formation occur, if there is a progressive increase in dilatation, renal function deteriorates more than 10% or ipsilateral function falls below 40%. Surgical treatment of UPJ obstruction aims to re-establish undisturbed drainage, preserve or improve renal function, prevent pyelonephritis, and eliminate symptoms. During the last years, laparoscopy and robot-assisted laparoscopy have been used more in addition to the open surgical techniques for the surgical treatment of UPJ obstruction.