Objectives: There is no formal agreement or criteria utilized to establish a standard of treatment in children with antenatally diagnosed HN. Methods: We analyzed our own experience in addition to the protocols attending to this subject. Twenty eight (28) children with unilateral HN were assessed from October 1999 through October 2005 and the anteroposterior diameter of renal pelvis (APDP) was measured. Results: Patients underwent surveillance with US and cintilography in 3, 6, 12 and 24 months. The treatment results were reviewed following the classification of Society of Fetal Urology: slight (2 to 5 mm), moderate (6 to 10 mm) and severe (>10-15 mm). Conclusions: We concluded that slight HN would never be operated on while the severe ones would always be. The moderate HN, on the other hand, would remain under surveillance with US and cintilography for two years.321010311034Helin, I., Person, P.H., Prenatal diagnosis of urinary tract abnormalities by ultrasound (1986) Pediatrics, 78 (5), pp. 879-882Raynor, B.D., Routine ultrasound in pregnancy (2003) Clin Obstet Gynecol, 46 (4), pp. 882-885Capello, S.A., Kogan Barry, A., Renal ultrasound has led to earlier detection and repair of ureteropelvic junction obstruction (2005) J Urol, 174 (4), pp. 1425-1428Ranjiv, M., Antenatal hydronephrosis current evaluation and management (2006) Indian J Urol, 22, pp. 10-14Koff, S.A., Neonatal management of unilateral hydronephrosis. Role for delayed intervention (1998) Urol Clin North Am, 25 (2), pp. 181-186. , May;Subramanian, R., Kouriefs, C., Dickson, A.P., Antenatally detected pelvi-ureteric junction obstruction: Concerns about conservative management (1999) BJU Int, 84 (3), pp. 335-338. , Aug;Ulman, I., Jayanthi, V., Koff, S.A., The long-term followup of new-borns with severe unilateral hydronephrosis initially treated nonoperatively (2000) J Urol, 164 (3 PART 2), pp. 1101-1105Chetin, B., Rolle, U., Puri, P., Does delaying pieloplasty affect renal function in children with a prenatal diagnosis of pelvicureteric junction obstruction? (2002) BJU Int, 90 (1), pp. 72-75Fernbach, S.K., Maizels, M., Conway, J.J., Ultrasound grading of hydronephrosis introduction to the system used by the Society for Fetal Urology (1993) Pediatr Radiol, 23 (6), pp. 478-480Harding, L.J., Malone, P.S., Wellesley, D.G., Antenatal minimal hydronephrosis: Is its follow up an unnecessary cause of concern? (1999) Prenat Diagn, 19 (8), pp. 701-705Zaccara, A., Marchetti, P., Sala, L., Are preoperative parameters of unilateral pielo-ureteric junction obstruction in children predictive of postoperative function improvement? (2000) Scand J Urol Nephrol, 4, pp. 165-168Chi, T., Vickie, A., Hiept, N., Increased echogenicity as a predictor of poor renal function in children grade 3 or 4 hydronephrosis (2006) J Urol, 157, pp. 1898-1901Dhillon HK. Prenatally diagnosed hydronephrosis: The Great Ormond Street experience. BJU Int 1998;81Suppl 2:39-44DeGrazia, E., Castagnetti, M., Cimador, M., Surgical or conservative treatment of congent hydronephrosis:Ten years' experience (2001) Minerva Pediatric, 51 (4), pp. 275-283Eskild, J.A., Gordon, I.F., Frokier, J., Congenital unilateral hydronephros: A review of the impact of diuretic renography on clinical treatment (2005) J Urol, 173 (5), pp. 1471-1476Coplen, E., Austin, P.F., Yan, Y.D., Jeffrey, M., The magnitude of fetal renal pelvic dilatation can identify obstructive postnatal hydronephrosis and direct postnatal evaluation and management (2006) J Urol, 176 (2), pp. 724-727Chertin, B., Pollak, A., Rabinowitz, R., Hain, D., Farkas, A., Conservative treatment of uretero-pelvic junction obstruction in children with antenatal diagnosis of hydronephrosis: Lessons learned after 16 years of follow-up (2006) Eur Urol, 49 (4), pp. 734-738