Aneurism of the vein of Galen is a complex arteriovenous malformation which is of multiply communications between of the vein of Galen and the cerebral arteries. It represents less than 1% of the cerebral arteriovenous malformations. Few cases using three-dimensional (3D) power and color Doppler ultrasound have been reported in the literature. We present a case of an aneurysm of the vein of Galen diagnosed at 25th week of pregnancy. We demonstrate the main findings of 3D power and color Doppler ultrasonography in this anomaly. A 36-year-old pregnant woman, gravida 3, para 2 was referred to our institution because of a midline cystic mass diagnosed in a previous ultrasonography undertaken at 24 weeks' gestation. The ultrasonographic finding consisted of a male fetus with a midline cystic mass, with positive flow detection by color Doppler and ventriculomegaly due to the compressive effects of the malformation. The 3D color and power Doppler ultrasonography allowed us to reconstruct the architecture of the vascular malformation, and it showed the spatial relationships of aneurysm of the vein of Galen with the other structures of the brain. Pregnancy was interrupted at 29 weeks' gestation because of presence of cardiomegaly. A male newborn survived for 36 hours only. The 3D ultrasound can be used as advent image technique in prenatal diagnosis of aneurysm of the vein of Galen.