Prenatal hydronephrosis (HN) refers to fetal dilation of the renal collecting system. Two grading systems are widely used to describe prenatal HN ‐ the semiquantitative Society for Fetal Urology (SFU) grading system and the measurement of antero‐posterior diameter (APD) of the renal pelvis in the transverse plane on US. Patients with prenatal HN may go on to develop complications related to their underlying pathology, including urinary tract infections (UTIs), urolithiasis, hypertension, renal scarring, and chronic kidney disease. The most common etiologies of prenatal HN include physiological HN, ureteropelvic junction obstruction (UPJO), vesicoureteric reflux (VUR), and primary nonrefluxing megaureter. Patient populations with higher UTI rates will benefit from more intensive investigation, follow‐up, and parental counseling. The chapter focuses on whether the presence of VUR had an impact on UTI rates. It expresses the selective use of voiding cystourethrogram (VCUG) testing in the situations where findings may alter patient management.