In prenatal ultrasound screening, internal hydrocephalus and intracranial bleeding of the fetus are considered as primary diagnostic signs for a congenital brain tumor. We report the prenatal sonographic diagnosis of a congenital glioblastoma due to acute fetal internal hydrocephalus in the 37th week of gestation. After birth, the tumor's hyperechoic appearance on ultrasound was indistinguishable from intracranial bleeding. Diagnosis of a congenital glioblastoma (WHO stage IV) was confirmed by subtotal tumorectomy in the 9th week of life. In the international literature, only 6 cases of prenatally diagnosed glioblastomas have so far been reported, all of which associated with sonographically diagnosed fetal hydrocephalus. Further sonographic signs for a brain tumor are the tumor mass itself, a polyhydramnion, enlarged biparietal diameters and head circumferences, as well as suspected intracranial bleeding.