54 neonates found to have pelvic dilatation on sonography are reported. They were studied by IVP, voiding cystography and renal function tests. Periodic sonography, urine cultures and DPTA furosemide in severe cases were performed during the follow-up (3-32 months). The ectasias were classified in 4 grades, found a good correlation with urography in grades I, III and IV. Neonatal pelvic dilatation is associated with: 1) urinary tract infection (17.4%); 2) vesicoureteric reflux (25.5%); 3) ureteropelvic obstruction (17.4%). During the follow-up 52% of ectasia disappeared (x: 6 months) and 11% will required pieloplasty (x: 10 months). It is noteworthy the high rate of initial and further urinary tract infection (53% of patients).