Background: Frequent alcohol use during the first 8 weeks of pregnancy can result in spontaneous abortion and dysmorphologic changes in the developing organ systems of the embryo, including the heart, kidneys, and brain. However, few population-based studies are available that describe the prevalence of frequent drinking (6 or more drinks per week) among women prior to and during early pregnancy (the periconceptional period), and the sociodemographic and behavioral factors that characterize these women. Such knowledge is fundamental to the design of targeted interventions for the prevention of fetal alcohol syndrome (FAS) and other prenatal alcohol-related disorders. Methods: This cross-sectional study used survey data collected by the National Center for Health Statistics as part of the 1988 National Maternal and Infant Health Survey (NMIHS). Weighted prevalence estimates were calculated using SUDAAN, and multivariate analyses were used to determine risk factors for frequent drinking. Results: Forty-five percent of all women surveyed reported consuming alcohol during the 3 months before finding out they were pregnant, and 5% reported consuming 6 or more drinks per week. Sixty percent of women who reported alcohol consumption also reported that they did not learn they were pregnant until after the fourth week of gestation. Risk factors for frequent drinking during the periconceptional period included 1 or more of the following: being unmarried, being a smoker, being white non-Hispanic, being 25 years of age or older, or being college educated. Conclusions: Half of all pregnant women in this study drank alcohol during the 3 months preceding pregnancy recognition , with 1 in 20 drinking at moderate to heavy levels. The majority did not know they were pregnant until after the fourth week of pregnancy, and many did not know until after the 6th week. Alcohol is a teratogen capable of producing a number of adverse reproductive and infant outcomes. Public health measures needed to reduce these potentially harmful exposures include alcohol assessment , education, and counseling for women of childbearing age, with referral sources for problem drinking, and family planning services for pregnancy postponement until problem drinking is resolved.