In the European part of the International Reflux Study in Children (7 participating centers) 151 infants and children were randomly allocated to surgical treatment of primary grades III and IV vesicoureteral reflux. Reimplantation was performed unilaterally in 65 patients and bilaterally in 86, for a total of 237 ureters reimplanted. The patients were followed at regular intervals for 5 years. Reflux was absent in 231 of the reimplanted ureters (97.5%) at the end of 5 years. No patient underwent reoperation for reflux. In 10 ureters (4.2%, 10 patients) obstruction developed postoperatively and 7 needed reoperation. All reoperations were performed on the left side. Of the obstructed kidneys new scars developed in 6 during the 5-year followup. Including these cases, the number of new renal scars was equal in the surgical and medical groups (20 each). The number of pyelonephritic episodes during followup was significantly less in the surgical group (without chemoprophylaxis) than in the medical group (on chemoprophylaxis). No kidneys were lost and no child became hypertensive. If voiding cystourethrography and excretory urography were normal 6 months postoperatively, the reflux had been permanently eradicated and postoperative obstruction could be ruled out. In this study the patients who underwent reimplantation had a 74% (112 of 151) chance of an uncomplicated postoperative course (no persisting reflux, obstruction, pyelonephritis or severe renal damage).