To analyze the current management recommendations among French-speaking physicians treating infants with antenatal renal pelvis dilatation, we surveyed 83 pediatric nephrologists and 68 pediatric urologists by questionnaire. A total of 45 (54%) pediatric nephrologists and 38 (56%) pediatric urologists responded. The threshold for the diagnosis of abnormal fetal renal pelvis dilatation was significantly higher among pediatric urologists than nephrologists. All responders perform renal ultrasound examinations after birth. Postnatal renal pelvis dilatation was considered abnormal if the anteroposterior diameter was >/=11+/-1.9 mm by the pediatric urologists and >/=9+/-2.9 mm by the pediatric nephrologists ( P=0.003). Pediatric urologists were more likely than nephrologists to recommend routine voiding cystourethrography [41% versus 20% ( P=0.04)]. Mercaptoacetyl-triglycine renography was the most routinely used tool to achieve functional evaluation during follow-up among the responders. Pediatric urologists were more likely to recommend surgical treatment in dilated kidneys with initial function <40%. In conclusion, pediatric urologists had significantly higher thresholds for the detection of prenatal and neonatal renal pelvis dilatation. They also more frequently recommended routine voiding cystourethrography and surgical therapy of dilated kidneys with low function than pediatric nephrologists. The variability in attitudes is most probably due to the absence of clear guidelines based on prospective and controlled trials.