Antenatal hydronephrosis is prenatal ultrasonography's most often detected urologic anomaly. Its etiology is quite variable ranging from mild abnormalities of the urinary system such as transient hydronephrosis to more significant ones such as ureteropelvic junction obstruction (UPJO) or high-grade vesicoureteral reflux (VUR). UPJO comprises the most encountered etiology of antenatal hydronephrosis with variable postnatal clinical scenarios ranging from complete resolution to the need for surgical intervention. The therapeutic approach for antenatal hydronephrosis caused by UPJO has undergone a dramatic shift from primary surgical intervention to initial conservation and elective surgery when indicated. Although there is a consensus that sustained increase in the grade of hydronephrosis, significant loss in differential renal function, and the existence of symptoms (such as recurrent UTI, nausea, vomiting, and cyclic flank pain) are reasonable indications of surgical need, precise cutoffs for the previous factors are still debated. This review aims to argue this debate and offer an overview of the antenatal and postnatal evaluation of antenatally detected ureteropelvic junction obstruction.