Seventy-six children with a total of 123 ureters showing vesico-ureteric reflux were reviewed in order to detect intrarenal reflux (pyelotubular backflow) occuring during micturating cystourethrography. This was found in 7 patients (9.2%). Five patients had unilateral and two bilateral intrarenal reflux. In only 7 out of the 9 kidneys with intrarenal reflux was it possible to outline the kidney contour precisely on excretion urography. In 3 cases renal damage corresponded exactly to the areas with intrarenal reflux. One kidney showed damage which did not correspond to the location of intrarenal reflux and 3 were without signs of damage. Renal damage of varying localization was found in 54 of the 123 kidneys with vesico-ureteric reflux and intrarenal reflux was present in 6 of these (11%). The significance of intrarenal reflux as a cause of renal damage and whether intrarenal reflux might be primary or secondary to the renal damage are discussed, and it is concluded that presence of intrarenal reflux is a definite indication for operation.