Objective: To examine serving size knowledge in African Americans and how it is related to body mass index (BMI). Design: Serving size knowledge of food commonly consumed by African Americans was assessed by asking the subjects to select the amount of food considered to be a single serving size by the United States Department of Agriculture and the Food and Drug Administration. Seventeen food items were tested, and the amounts selected were weighed. Body mass index was estimated from measured height and weight. Setting: Churches. Participants: Ninety-five African American women. Main Outcome Measures: Amount of food selected and BMI. Analyses: The amount of food selected was compared with the respective standard serving using the 1-sample Wilcoxon signed rank test. The association between BMI and the amount selected was assessed by logistic regression. Results: The subjects significantly overestimated (P = 0.001 to 0.02) serving sizes for cornflakes, apple, watermelon, butter, whole milk, chips, and regular soda. Body mass index was significantly associated with overestimation of cornflakes, butter, cookies, and macaroni and cheese (P = 0.01 to 0.03), and the odds ratio for overestimating these food items was 1.46-1.65 times greater per 5-unit increase in BMI. Conclusions and Implications: African American women overestimated the serving sizes for 7 of the food items tested, and 4 of the estimates were correlated with BMI. Education regarding serving size is recommended for certain food items. (Contains 3 tables and 1 figure.)