The risk of fetal alcohol syndrome (FAS) is known to increase with Increased maternal age and parity. This study investigated the hypothesis that the deficits in growth and intellectual function seen in non-FAS infants exposed to alcohol at moderate-to-heavy levels are also found disproportionately in the offspring of older mothers. Mothers of 480 African-American, inner-city infants were interviewed at each prenatal clinic visit regarding their use of alcohol during pregnancy. Infants were assessed for physical growth and cognitive development repeatedly through age 13 months. In analyses run separately for the infants of younger and older mothers, alcohol-related deficits were seen most strongly in the offspring of women over 30 years of age. This pattern was not caused by lower levels of drinking by the younger mothers. Age-related increases in maternal body fat-to-water ratio and a faster rate of alcohol metabolism in chronic drinking women may account for the greater vulnerability of the offspring of the older mothers. These data suggest that physiological changes associated with aging and/or chronic drinking may play an important role in the alcohol-related birth defects seen in infants exposed at moderate-to-heavy levels.