We evaluated real-time ultrasonography in the diagnosis of vesico-ureteric reflux by comparing its findings to those of dynamic micturition cystourethrography. The study material comprised 124 consecutive infants and children referred to uroradiological workup, usually because of a relapsing febrile urinary tract infection. Both examinations were done during the same session. Consistent findings were obtained on 232 ureters, of which 37 displayed II. and 19 III. + reflux. II. reflux was found in 12 ureters by cystography only; thus one-fourth of low-grade refluxes escaped the diagnosis by ultrasound. The false negative findings of ultrasound examination included also two ureters showing III. reflux in cystography. As calculated for therapy-requiring (grade III or higher) reflux, the sensitivity of ultrasound was 90 per cent and its specificity 100 per cent. We conclude that ultrasound can be used as a primary diagnostic technique for girls, and in the follow-up of both boys and girls.