The purpose of this study is to detect new urinary biomarkers that can be used as predictors on renal function in congenital hydronephrosis caused by unilateral ureteral obstruction (UUO) and to elucidate the pathophysiology of UUO.

Inclusion Criteria:

• Children referred to surgical treatment of congenital hydronephrosis caused by ureteral obstruction.
• Declining function of the hydronephrotic kidney more than 5 %, and to less than 40 % of the total renal function OR ipsilateral flank pain.

Exclusion Criteria:

• Bilateral hydronephrosis
• Previous operation in the urinary system except operation for phimosis and other deformations of the external genital organs.
• Deformations in the lower part of the ureter, bladder and urethra. Urinary stones. Reflux. Urinary tract infections < 6 months.
• Neurogenic bladder dysfunction.
• GFR < 40 % standardized to age.
• Non-compliance. Linguistic difficulties.

Children referred to surgical treatment of congenital hydronephrosis caused by ureteral obstruction.