Acquired ureteropelvic junction obstruction in childhood.

Ureteropelvic junction (UPJ) obstruction is generally considered to be a congenital lesion or occasionally an intermittent phenomena relating to periods of increased urine flow. Acquired ureteropelvic junction obstruction without a recognizable secondary cause is quite unusual. We present a 5.5-year-old boy who, 4 years after repair of a right sided UPJ obstruction, developed a significant left-sided UPJ obstruction in a system which previously had been normal.