Background Prenatal Hydronephrosis is diagnosed in 1–5% of pregnancies worldwide. The diagnosis of antenatal hydronephrosis (ANH) causes stress to the parents and dilemmas to the paediatrician.

Objectives To examine the correlation between the degree of the renal pelvic dilatation (RPD) detected by the first 2–5 days of life and the postnatal outcome. To investigate the correlation between bilateral hydronephrosis and the nephrologic outcome. To discuss the possibility of decreasing the postnatal examinations of these healthy babies.

Methods During a period of two years, we enrolled 143 term newborns with ANH. These babies had an ultrasound at the age of 2–5 days and a second ultrasound at the age of 4–6 weeks. After the examinations they were referred to our nephrologist.

Results Out of 8370 live-births, 143 infants had ANH. Six babies never completed the exam. At the first exam 69 babies were normal, 62 babies had mild, 3 babies had moderate and 3 babies had severe RPD. On their second ultrasound 76 had normal findings, 36 had mild, 8 had moderate and 12 had severe RPD. 132 babies completed both of the examinations. Bilateral hydronephrosis was detected in 33 cases during their first ultrasound while on the second only 27. There were 11 infants with UPJ obstruction 9 of them with severe RPD. We found 10 babies with VUR. Six babies needed surgical intervention.

Conclusions There seems to be a correlation between the degree of RPD and the presence of postnatal pathology. Bilateral hydronephrosis probably carries increased risk for postnatal pathology.