The purpose of this study was to examine the usefulness of the self-administered modified Willett food frequency questionnaire (mWFFQ) relative to duplicate 24-hour recall interviews as a dietary assessment tool during pregnancy. Fifty healthy pregnant women living in the upper Midwest were recruited for the study. At gestational weeks 16 and 21 (second trimester) and 30 and 35 (third trimester) the women were interviewed at home; they provided oral responses concerning their food and beverage consumption during the previous 24 hours. At weeks 21 and 35, immediately following the interviews, the women were asked to complete an optically scannable food frequency questionnaire, modified to evaluate daily food consumption during a 2-month time period (mWFFQ). Kilocalories and seven nutrients were computed from all dietary data, based on USDA Handbooks 8 and 456. Regression analyses were performed between nutrient intake from the 24-hour recall averages and the nutrient data generated by the mWFFQ, with the timesters serving as independent time periods. According to our preset criterion, correlation coefficients indicated that the assessment tools were comparable during the third but not the second trimester. During both trials, the mWFFQ provided consistently higher kilocalorie and nutrient values than did the 24-hour recall with the exception of fat intake. Based on our findings we conclude that the mWFFQ is a useful tool for assessing nutrient intake of groups of pregnant women, but that familiarity with the characteristics of the participants and the instrument may be important to data interpretation.