The urinary tract obstruction may depend by: ureteropelvic junction obstruction, vesicoureteric reflux, posterior urethral valves, megacystis-microcolon syndrome. Hydronephrosis accounts for 75% of prenatally diagnosed fetal renal abnormalities with, in many cases, renal dysplasia, oligohydramnios and Potter's sequence. With ultrasound is possible to diagnose most urinary tract obstructions that occurs in 1% of all pregnancy, but only 0.2% have clinical relevance. We have conceived an ultrasonographic protocol to evaluate the renal and urinary tract morphology, the cystis, the amniotic fluid and the external genitalia for a more easy ultrasonographic diagnosis and for the exact pre and postnatal management.