Radioisotope scintigraphy of the kidney and i.v. urography were compared in 79 children with bacteriologically proven urinary tract infections, followed up between 1 and 4 yr. Both techniques were in agreement as to the presence or absence of an abnormality, and the extent of any abnormality present, in 93.5% of the kidneys. There was a discrepancy in 10 kidneys. Excretion urography has a sensitivity of 0.86 and a specificity of 0.92 in the detection of pyelonephritic scarring in children. Radioisotope scintigraphy has a sensitivity of 0.96 and a specificity of 0.98. Radioisotope scintigraphy is the preferred technique.