Background: The influence of portion size on children's intake and self-regulation of food has gained attention; however, few studies have examined portion sizes in school lunch. This study investigated kindergarteners' intake when they were given different entree portion sizes from the lunch menu. Methods: Plate waste was used as a proxy to measure intake. A standardized lunch of chicken nuggets, rice, green beans, applesauce, and milk was served every Tuesday for 5 consecutive weeks at a Kinder Center. All menu items and the self-selection of 2, 3, or 4 nuggets were served the first week as a pilot. In the second and fourth weeks, trained servers preportioned kindergarteners' plates with 4 nuggets. In the third and fifth weeks, kindergarteners verbally self-selected 2, 3, or 4 chicken nuggets. A Mann-Whitney test was used to determine a significant difference in intake between the 2 days kindergarteners were allowed to select the portion size and the 2 days they were preportioned. Results: A significant difference (p less than 0.009) in intake was found between the self-selection of entree portion size and the preportioned entree regardless of sex or whether kindergarteners attended the AM or PM session. No significant difference was found in milk, fruit, vegetable, or rice intake between choice and nonchoice lunches. In this study, kindergarteners ate more chicken nuggets when they were offered a larger portion size. Conclusions: Further investigation is needed on the impact of letting kindergarteners self-select portion sizes, and the potential negative outcomes of larger portion sizes on children's caloric consumption in elementary schools. (Contains 2 figures.)