The term portion size is used differently by food manufacturers, regulatory agencies, and consumers. As such, it is unclear how information about portion size may influence perceived satiety and intake of foods by consumers. The objective of this study was to examine how portion size information influences satiety and intake, and how consumers interpret the term portion size. A randomized controlled design was used in which subjects were served a lunch meal consisting of a preload of pasta followed by ad libitum servings of the same pasta. In each of three separate sessions the subjects were told that the preload meal constituted 1/2, 1, or 1 1/2 portions of pasta. Thirty-three normal-weight subjects (22 males and 11 females) were recruited from a 250-member volunteer employee panel at Natick Research, Development, and Engineering Center during January 2005. Main measures were pre- and post-preload hunger/fullness ratings, liking ratings, amount consumed of the pasta after the preload, and Likert ratings of statements about different definitions of portion size. Results showed that portion size information did not influence satiety ratings or total intake. Consumers associated portion size more with daily nutrient requirements than with an ideal quantity for a satiating meal (P<0.01). Information about portion size may not be a good tool to manipulate food-intake behavior. Consumers' concept of portion size is associated more with objective measures of food than with personal experience about the amount that would be appropriate to eat.