Three hundred and eleven patients diagnosed to have congenital hydronephrosis proven by postnatal ultrasonography in a ten-year period between 1987 and 1996 were studied retrospectively. These were classified into mild degree of hydronephrosis in H (64%), moderate in 94 (30%) and severe in 18 (6%) patients, according to first post natal sonography and depending on the measurement of the anterio-posterior transverse diameter of the pelvi-calyceal system. Significant obstructive uropathy was documented in 66 patients by Technetium-Diethylene triamine penta acetic acid renogram (Tc99m DTPA Renogram Vesicoureteric reflux was found in 22 patients by voiding cysto-urethrogram. On follow-up the hydronephrosis regressed spontaneously in 99 (31.8%), was stable in 167 (53.6%) and needed operative intervention in 45 (14.4%) patients. The types of surgical operations were pyeloplasty in 49% and ureteric re-implantation in 27%. Fifteen (83%) of the children with severe hydronephrosis and 32 (34%) of the moderate hydronephrosis group were operated o while none of the children with the mild form required operative intervention. We recommend ultrasound follow-up for mild hydronephrosis and a coordinated approach and work-up for congenital moderate and severe hydronephrosis. Surgery should only be considered if renal function is affected.