Of 49 children with renal ectopy, 25 (51%) had hydronephrosis on excretory urography. Dilatation of the renal pelvis was the result of primary ureteropelvic junction obstruction (17 children), significant vesicoureteral reflux (6 children), or extrarenal pelves and calices with renal malrotation producing apparent ureteropelvic junction obstruction (2 children). Vesicoureteral reflux was a common finding in these patients, occurring in 52% of those with crossed renal ectopy and in 70% of those with pelvic kidney. The need for surgical intervention results from either (1) ureteropelvic junction obstruction secondary to high insertion of the ureter on the renal pelvis or (2) vesicoureteral reflux secondary to aberrant migration of the lower ureter. Most children with renal ectopy and ureteropelvic dilatation require surgical reconstruction at the renal level. In selected patients, ureterocalicostomy is an attractive alternative to conventional pyeloplasty and appears to afford improved drainage with superior results.