Primary vesicoureteric reflux (VUR) is the most common urological abnormality in children, with a prevalence of approximately 1%. It may be an isolated finding, due to an abnormal length of the submucosal portion of the lower ureter and/or abnormal location of the ureteral orifice. In a significant number of cases, VUR is diagnosed after urinary tract infection (UTI). Antenatally diagnosed hydronephrosis lead to the suspicion of VUR in many newborn babies, more commonly boys.

Greyscale imaging and Color Doppler mode can show indirect or direct signs for reflux but their sensitivity remains low. Voiding urosonography (VUS) is based on the administration of an ultrasound contrast-agent after bladder catheterization. Reflux is diagnosed when echogenic microbubbles are demonstrated in one or both ureters and/or the pelvicaliceal system. It is graded into 5 classes, as done for the radiological retrograde cystography (VCUG).

Since 1996, more than 60 publications have emphasized the interest of VUS. VUS allows a higher rate of reflux of approximately 9%, compared to VCUG, with a trend to overgrade reflux. According to the 2008 EFSUMB Guidelines, the common selection criteria for VUS include: 1. Follow-up examination for reflux after conservative or surgical therapy; 2. First reflux examination in a girl; 3. Screening for reflux e.g. siblings, transplant kidney.

However, the place of VCUG and consequently VUS is now decreasing in the follow-up of patients without complications, as many refluxes, mainly of low grades, have shown to disappear spontaneously during the first years of live.