The renal findings revealed by intravenous urography (IVU) in 306 children (73 boys, 233 girls) are reported. The children were seen at eight European centres and enrolled in an international study comparing medical and surgical management of children with urinary tract infection and severe vesico-ureteric reflux who were followed for 5 years. In all, 155 children were randomly allocated to medical and 151 to surgical treatment. The protocol and the investigative techniques were standardized, and randomization, data collection and analysis were performed centrally in Essen, Federal Republic of Germany. At entry 149 (49%) had established renal scarring (79 medical, 70 surgical). Presence of normal kidneys (105), areas of thinned parenchyma (52) and grade of reflux were also evenly distributed. IVU was repeated at 6, 18 and 54 months, and serial urine culture, 99mtechnetium-dimer-captosuccinic acid scans and plasma creatinine estimations were performed. Follow-up was complete in 272 children (89%). In 174 children (57%: 90 medical, 84 surgical) there was renal growth without morphological change. New renal scars developed in 19 children treated medically and 20 treated surgically; 12 (5 medical, 7 surgical) developed in previously normal kidneys. Six followed postoperative obstruction. No significant difference in outcome was found between medical and surgical management in terms of the development of new renal lesions or the progression of established renal scars.