Chronic pyelonephritis is a disease of childhood which is carried on into adult life. Children under the age of 4 in whom UTI, vesico-ureteric reflux and pyelotubular back-flow coexist appear to be particularly at risk of developing kidney damage. Attempts to prevent kidney damage in adults by detection and treatment of covert UTI are doomed to failure because persistent bacteriuria in the adult is a consequence of underlying abnormality of the urinary tract rather than its cause. Our main hope for the prevention of kidney damage associated with bacteriuria and reflux is to detect and treat these conditions at the earliest possible age.