Measuring the extent to which individuals meet the 5 A Day dietary recommendation for fruits and vegetables can provide information on the effectiveness of public health efforts to increase consumption of these foods. However, dietary measurement is complicated by the issue of serving size. We compared two methods of measuring fruit and vegetable consumption using a random-digit-dialed telephone survey of 917 Washington state adults. The survey included two sets of questions about fruit and vegetable consumption, one providing and the other not providing standard definitions of serving size. The specific wording of questions had a large effect on the conclusions about levels of fruit and vegetable consumption. Although only 26% of respondents met the 5 A Day recommendations without serving size information, 50% met these recommendations when using a measure that included a definition of serving size.