With the widespread use of obstetric echography the incidence of fetal hydronephrosis has been reported more frequently. Consequently, many uropathies have been detected in asymptomatic neonates. The authors report their experience with prenatally detected primary non-refluxing megaureter. Newborns with fetal hydronephrosis were investigated by ultrasonography and micturating cystourethrogram after the beginning of chemoprophylaxis. If primary megaureter was identified, after 1 month the children underwent 99tm-DMSA, diuretic 99tm-DTPA, and intravenous urography. Eight infants with primary megaureter (bilateral in 3 cases) were identified, for a total of 11 renal units for study. All children were submitted to non-operative management. We performed ultrasonography and diuretic 99tm-DTPA during follow-up, which lasted on average 75 months. The mean cross-sectional diameter of the dilated ureter was 13.6 mm during neonatal period, and reached 8.4 mm at the end of follow-up. The renal function and the diuretic renogram remained stable throughout follow-up. Two neonates presented transitory hypertension. Our results support the notion that conservative management is safe for primary megaureter detected in asymptomatic neonates, with most cases showing spontaneous regression during a prolonged follow-up.