OBJECTIVE: To evaluate the clinical use of hourly fetal urine production rate (HFUPR) in polyhydramnios. METHODS: This was a retrospective review of 33 singleton pregnancies with polyhydramnios, 30 of them unexplained and three due to gastrointestinal atresia. HFUPR was estimated using three-dimensional ultrasound and was compared with recently established nomograms. Abnormal midterm outcome, defined as diagnosis or persistence of pathology after the neonatal period until the age of 2 years, was analyzed according to prenatal HFUPR measurements and other polyhydramnios characteristics. RESULTS: Seventeen of the 30 fetuses with unexplained polyhydramnios had an HFUPR above the 95(th) centile, and five (29.4%) of them developed midterm disorders. None of the 13 with normal HFUPR developed midterm disorders. The HFUPR was 1.9 (SD, 0.7) multiples of the median (MoM) in fetuses with an adverse childhood outcome and 1.4 (SD, 1.2) in fetuses with normal childhood outcome (P = 0.34). In the three fetuses with gastrointestinal atresia, the HFUPR was significantly lower than in those with unexplained polyhydramnios (P = 0.003). CONCLUSION: HFUPR was associated with the mechanism of polyhydramnios but failed to help in the prognosis of unexplained polyhydramnios because of lack of power. Children with prenatal unexplained polyhydramnios and HFUPR above the 95(th) centile should nevertheless receive detailed pediatric follow-up.