Patients with congenital hydronephrosis will be identified by inpatient consultations performed by Dr. Assadi for congenital hydronephrosis and by outpatient problem lists with congenital hydronephrosis of Dr. Assadi's existing patients. Once identified, the patient's grade of hydronephrosis will be recorded from initial ultrasound based on Society of Fetal Urology (SFU) classification. If no initial SFU classification was assigned to the hydronephrosis a pediatric radiologist will review the initial ultrasound images and classify the grade of hydronephrosis based upon SFU criteria. The patients ensuing evaluation of their hydronephrosis that took place will then be recorded and de-identified. Data to be collected will include: Ultrasound evaluations of the abdomen, retroperitoneum, or renal system, Voiding Cysto-Urethrogram (VCUGs), nuclear studies: diuretic enhanced technetium-99m dietylene triamine penta-acetic acid renogram (DTPA) or technetium-99m Mercapto-acetyl-triglycine renogram (MAG3), referral to pediatric urology for pyeloplasty, serum electrolytes, Blood Urea Nitrogen (BUN) and creatinine, urinalysis, urinary tract infections, and placement on long-term antibiotic prophylaxis.