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Despite the field's longstanding concern with underreporting of alcohol consumption, traditional survey questions encourage error because respondents often must calculate their number of drinks based on standard drink sizes that often do not match their own drinking style. This study considered how often respondents' self-defined drink sizes matched a 'standard' drink size based on approximately 12 g of ethanol for six different beverages. We also studied whether respondents could accurately judge the size of their drinks. Subjects were recruited and interviewed at urban prenatal clinics, health clinics, and via snowball referrals and community outreach in Los Angeles and the San Francisco Bay Area. Because of the urgency of accurate measurement of consumption during pregnancy, urban pregnant women from the groups most at risk for Fetal Alcohol Syndrome, Native Americans (n = 102) and African Americans (185), were targeted. A small comparison group of urban pregnant white women (n = 34) was included. One-hour in-person interviews were conducted. Self-defined drink sizes were determined for each beverage consumed, using models and photographs of vessels. Frequent drinkers and the majority of women who reported drinking higher alcohol content beverages reported drinking larger-than-standard drink sizes. The median size of a malt liquor drink among the daily drinkers was almost three times as large as the standard, their fortified wine drinks were four times the standard, and their spirits drinks were six times the standard size. The majority of drinkers of each beverage were unable to accurately judge the size of their drinks, underestimating the number of fluid ounces by about 30%. Although the vessels methodology used here must be refined and tested further on other populations (e.g., men, nonpregnant women, and all ethnic groups), results suggest that determination of risk levels should be based on survey data that takes into consideration the beverage mix and the actual size of respondents' alcohol drinks.