The main findings of the IRSC after 5 years of observation are summarized. Of the 434 children entered 128 were from centers in America and 306 from Europe. They were randomly allocated and stratified to a medical or surgical regimen. Of the children 50% had scarred kidneys at entry evenly distributed between the groups. After 5 years of observation there was no difference in outcome between the 2 treatment groups in terms of renal size and growth, the development of new radiological renal scars or areas of parenchymal thinning, or of progression of established scarring. In Europe infection recurred in equal numbers of children but pyelonephritic symptoms were more common in the medical group. Nevertheless, new scars developed in 19 of 155 children treated medically and 20 of 151 children treated surgically, including 5 and 7, respectively, with previously normal kidneys. Factors influencing the choice of treatment include patient age, availability of expert surgical care and experienced medical supervision, parental choice and compliance. Followup studies indicate that renal scarring rather than persistence of reflux determines the prognosis and, therefore, emphasis should be placed on the prevention of scarring.