Aims: To examine the effect of maternal alcohol use during pregnancy on infant behavioral outcomes and birth weight, and to investigate the differential susceptibility of infant behavioral outcomes and birth weight to prenatal alcohol exposure. Methods: Data on children born to women taking part in the United States National Longitudinal Survey of Youth (NLSY) (n = 1618) were analyzed using the sibling fixed-effects model, which helps adjust for maternal, genetic and social confounders when examining effects of pre-natal exposure to possible toxins such as alcohol. Mothers were classified as non-drinkers, light-to-moderate drinkers and heavy drinkers according to their frequency of alcohol use during pregnancy. Infants' behavioral outcomes were assessed using the modified Rothbart Infant Behavior Questionnaire in the NLSY, which measures three dimensions of behavioral outcomes: positive mood, fearfulness and difficultness. Results: Estimates from the model indicated that drinking during pregnancy was positively associated with infant difficultness, but not with positive mood or fearfulness. Further analysis by frequency of alcohol use suggested that both light-to-moderate and heavy drinking were associated with an increase in infant difficultness. Additionally, while low-to-moderate drinking during pregnancy was associated with infant difficultness, drinking at this level was not associated with low birth weight. Conclusion: The findings suggest that maternal alcohol use during pregnancy is a risk factor for infant behavioral outcomes, after taking into account many confounding factors. Infant behavioral outcomes appear to be more vulnerable to light-to-moderate levels of alcohol use during pregnancy than birth weight is.