OBJECTIVES: To set up a fetal lamb model for intrauterine fetal urodynamic studies. METHODS: Fourteen fetal lambs underwent placement of a bladder catheter at a mean gestational age of 87 days. Three fetuses also had a partial urethral obstruction by the simultaneous placement of a peri-urethral constricting ring. Urodynamic and ultrasound studies were performed weekly by the filling cystometry method. RESULTS: Hundred and six voiding cycles were recorded during 25 urodynamic studies between 84- and 133-days gestation. All voiding profiles were biphasic with a mean duration of 4.2 min (range 1-10), a mean voiding pressure of 23 cm of water (range 7-33) and a mean periodicity of 19.2 min (range 11-50). The obstructed animals had bladder overactivity. This correlated with ultrasound and post-mortem findings of megacystis and bilateral hydroureteronephrosis. The fetal mortality rate was 85.7% and the mean duration of survival post surgery was 45 +/- 5.7 days. CONCLUSION: Serial urodynamic studies could be performed in a fetal lamb model. Following partial urethral obstruction, bladder overactivity was observed.