Morphology of the cerebral cortex was studied in fetuses on gestational Day 21 following oral administration of several doses of ethanol (for total doses of 10,15, or 18 g/kg) to pregnant rats on gestational Days 14 and 15, a critical period for the development of the cerebral cortex. All doses of ethanol were associated with a reduction in maternal weight gain, fetal body weight, and placental weight. Only the high dose of ethanol (total dose 18 g/kg) caused significant fetal cortical thinning. Acute exposure of pregnant rats to ethanol produced dose-dependent malformations of the cerebral cortex and hippocampus in fetuses. On gestational Day 21, the 18 g/kg group contained fetuses with severely disorganized cortical architecture, heterotopias of the cerebral cortex, pia and choroid plexus, and status verrucosus deformis. Fetuses from the 10 g/kg group had less severe malformations, such as disorganization of layers of cortical neurons and dentate granule cells while fetuses from the 15 g/kg group had a mixture of severe and minor malformations. This study demonstrates that acute ethanol exposure during a critical period of development in rats can result in brain malformations similar to those reported in human fetuses and neonates from alcoholic mothers.