Aneurysms of the vein of Galen (AVG) represent less than 1% of all intracranial arteriovenous malformations. Two cases of prenatal diagnosis made by color Doppler ultrasonography at 32 weeks of gestation are reported. Both cases presented with antenatal mild cardiomegaly and both developed severe cardiac failure in the neonatal period. Embolization was unsuccessful and both infants died. These cases highlight the need for a careful evaluation of the time and mode of delivery; embolization must be performed after a fully informed decision.