OBJECTIVES: The primary objective is to determine whether intrauterine vesicoamniotic shunting for fetal bladder outflow obstruction, compared with conservative, noninterventional care, improves prenatal and perinatal mortality and renal function. The secondary objectives are to determine if shunting for fetal bladder outflow obstruction improves perinatal morbidity, to determine if improvement in outcomes is related to prognostic assessment at diagnosis and, if possible, derive a prognostic risk index and to determine the safety and long-term efficacy of shunting. DESIGN: A multicentre randomised controlled trial (RCT). SETTING: Fetal medicine units. POPULATION: Pregnant women with singleton, male fetus with isolated lower urinary tract obstruction (LUTO). METHODS: Following ultrasound diagnosis of LUTO in a male fetus and exclusion of other structural and chromosomal anomalies, participation in the trial will be discussed with the mother and written information given. Consent for participation in the trial will be taken and the mother randomised via the internet to either insertion of a vesicoamniotic shunt or expectant management. During pregnancy, both groups will be followed with regular ultrasound scans looking at viability, renal measurements and amniotic fluid volume. Following delivery, babies will be followed up by paediatric nephrologists/urologists at 4-6 weeks, 12 months and 3 and 5 years to assess renal function via serum creatinine, renal ultrasound and need for dialysis/transplant. MAIN OUTCOME MEASURES: The main outcome measures will be perinatal mortality rates and renal function at 4-6 weeks and 12 months measured via serum creatinine, renal ultrasound and need for dialysis/transplant. FUNDING: Wellbeing of Women. ESTIMATED COMPLETION DATE: September 2010. TRIAL ALGORITHM: [flowchart: see text].