Pressure pop-off mechanisms are generally protective of overall renal function in newborns with posterior urethral valves. We describe atypical upper tract preservation with massive in utero extravasation and posterior urethral valves. CASE REPORT A 29-year-old GIIIPII woman underwent ultrasound at 31 weeks of gestation to investigate a discrepancy between fundal height and estimated gestational age. No genitourinary or other anomalies were evident on a 21-week ultrasound. The second study revealed a male fetus with significant oligohydramnios, bladder distention, ascites and a “keyhole” deformity of the posterior urethra. The right kidney had multiple cysts, echogenic parenchyma and a large perinephric fluid collection (fig. 1). The left kidney had mild pelvic dilatation. Serial aspirations of the perinephric urinoma and bladder confirmed favorable electrolytes. After weighing the pulmonary ramifications of severe oligohydramnios and pre-term delivery, cesarean section was planned for 35 weeks of estimated gestational age. A vesicoamniotic shunt was not placed due to late gestational age and an anterior placenta. The day before delivery 600 ml. of ascites were aspirated. After delivery the child required jet ventilation for 9 days. A urethral catheter was placed, and percutaneous aspiration of the perinephric urinoma and ascites decompressed the abdomen. A cyclic voiding cystourethrogram confirmed posterior urethral valves and grade V reflux on the left side only