Heavy alcohol consumption during pregnancy has been consistently associated with inhibited intra-uterine growth; however, the effect of social drinking is not yet clear. The relationship between moderate drinking and low birth weight (< 2,500 g) among a nationally representative sample of white married mothers who gave birth to singletons infants in the National Natality Survey (1980) is analysed here. Alcohol consumption during pregnancy was significantly associated with birth weight (p <0.02). Moreover, there was a gradient of risk in low birth weight associated with increasing amount of alcohol ingestion during pregnancy. There was a significant association between the mean birth weight of the singletons across different categories of alcohol intake (p< 0.0001). The difference between the mean birth weight of the singletons among moderate drinkers compared with nondrinkers was also statistically significant (p< 0.005). These relationships remained after simultaneously adjusting effects of the confounding variables gestational age, parity, smoking, weight gain, maternal age and education in multiple regression analyses. These findings confirm earlier reports of a relationship between alcohol use during pregnancy and decreased birth weight. Additionally, it is shown here that for moderate alcohol use during pregnancy, there is an adverse effect on the birth weight.