One hundred children with a proven urinary tract infection were studied prospectively using both ultrasound (US) and 99mTc dimercaptosuccinic acid (DMSA) scintigraphy to assess the efficacy of US in the detection of renal scarring. Sixty-nine girls and 31 boys with an age range of 0.5-11.8 years were studied. DMSA scintigraphy detected 19 scarred kidneys in 17 children. Scarring was classified as mild, moderate or gross. US detected a total of seven of the scarred kidneys (sensitivity 37%). US detected 0/6 kidneys with mild scarring, 1/7 kidneys with moderate scarring and 6/6 kidneys with gross scarring. Four kidneys with scarring on DMSA showed abnormalities other than scarring on US. 8/19 scarred kidneys were thought to be normal on US. It is important to detect renal scarring in young children and US cannot be relied upon for this purpose. It should therefore be supplemented with DMSA scintigraphy.