Morphologic alterations of fetal rat cerebral cortex were quantified by morphometric analysis following acute ethanol exposure on Gestational Day 14, a critical period of development of cerebral cortex. Pregnant rats were intubated with a total dose of 9 g/kg of ethanol on Gestational Day 14. Maternal blood ethanol levels ranged from 51 to 202 mg% during the period of ethanol exposure. Fetal brains were examined on Gestational Day 15, 24 h after the last dose of ethanol. The acute morphologic changes associated with ethanol exposure include enlargement of subventricular zone nuclei, cortical swelling, and dilation of pial blood vessels over the affected cortex. In some fetuses, cortical swelling was accompanied by the protrusion into the lateral ventricles of cytoplasmic blebs of ventricular zone cells. It is concluded that maternal ethanol exposure during a critical period of brain development produces measurable morphologic changes in fetal rat cerebral cortex within 24 h after ethanol exposure.