Two cases of congenital brain tumors were detected during routine antepartum sonography at the Mount Sinai Medical Center Perinatal Ultrasound Unit. In both cases, diagnosis was made during the third trimester at 31 and 33 weeks, respectively. In one of these patients, no intracranial abnormalities were noted on a sonogram performed in conjunction with genetic amniocentesis at 18 weeks gestation. The histologic diagnosis of both tumors was glioblastoma multiforme grade III. Previous reports describing the prenatal sonographic diagnosis of intracranial tumors have been in cases with fetal intracranial teratomas.