Up to 2% of live births in the United States have prenatal hydronephrosis (PHN) or urinary tract dilation (UTD). Next to cardiac anomalies, UTD is the second most common congenital anomaly. Causes of UTD include urinary tract obstruction, vesicoureteral reflux, and transient dilation. Most children born with UTD will not require surgical intervention. However, some children with UTD are at higher risk of developing renal and urologic disease. The purpose of this chapter is to review evaluation and workup of UTD, discuss risk stratification of UTD, and indications for lower tract imaging.