The teratogenicity of alcohol has been demonstrated in humans through clinical studies, behavioral studies, and epidemiologic studies, and in animals through controlled laboratory experiments. In humans exposed to alcohol during gestation the effects can range from fetal alcohol syndrome in some offspring of chronic alcoholic women to reduced average birth weight in offspring of women reporting an average consumption of two to three drinks or more per day. The behavioral effects of such exposure may range from mental retardation in children with fetal alcohol syndrome to milder developmental and behavioral effects in infants born to social drinkers. In animals, exposure to alcohol in utero may result in death, malformation, and growth deficiency as well as behavioral and developmental abnormalities. The mechanisms of impairment and related risk factors are yet to be elucidated.