Early diagnosis of urinary tract anomalies means an antenatal diagnosis, which is made more and more frequently thanks to the modern investigation methods. Even so, in our country there are many cases of belated diagnoses. A more frequent anomaly which could be diagnosed from the intrauterine period is hydronephrosis. Hydronephrosis may be caused by: obstruction, vesico-ureteral reflux, reno-ureteral duplication, ectopic ureter, ureterocele, posterior urethral valves, Prune-belly syndrome, etc. Idiopatic hydronephrosis constitutes the largest group. Defines of etiology and final management of congenital hydronephrosis are usualy made postnatally and it is very important to be done as soon as possible, because the increased pressure in the pyelons may cause damage of renal function and the repeated urinary tract infection may lead to renal failure. Considering these, we believe that it is important to develop a diagnostical algorithm for early and precise diagnosis and for proper management.