Exposure to ethanol during prenatal development can have devastating consequences on developing fetuses, the so-called fetal alcohol spectrum disordres (FASD). Among FASD, cases that exhibit all of three criterion; 1) central nervous system dysfunction, 2) prenatal and postnatal growth deficiency, and 3) characteristic cranial/facial abnormalities, referred as fetal alcohol syndrome (FAS). Children born to drinking mothers may suffer from severe brain damage that is expressed by a variety of behavioral alterations. We examined the effects of ethanol exposure during brain development on brain morphogenesis and circadian rhythm using a rat model. Pregnant Sprague-Dawley (SD) rats were fed a liquid diet containing 2.5-5.0% (w/v) ethanol during gestational days 10 to 21. Mean daily ethanol consumption by these dams was 11.53 +/- 2.54 g/kg/day. In rats prenatally exposed to ethanol, ectopias on the cerebral cortex, aberrant distribution of hippocampal mossy fibers, and fusion of cerebellar folia were found. Rats exposed to ethanol during the prenatal or postnatal period suffered from a fragile synchronizing system of circadian rhythms in adulthood. Although the prevalence of FAS in Japan is lower than in the United States, the increasing number of Japanese women with the drinking habit are cause for great concern. However, the preventive action of FAS/FASD has been advanced recently, and now alcoholic beverages carry labels warning of the risk of drinking during pregnancy and breastfeeding of babies. Although little is still known about how ethanol affects brain development, the only and most certain way to prevent FAS/FASD is total abstinence from alcohol during pregnancy and breastfeeding.