OBJECTIVE: To identify dietary factors related to the risk of gaining weight outside recommendations for pregnancy weight gain and birth outcome.Design:An observational study with free-living conditions.Subjects:Four hundred and ninety five healthy pregnant Icelandic women. METHODS: The dietary intake of the women was estimated with a semiquantitative food frequency questionnaire covering food intake together with lifestyle factors for the previous 3 months. Questionnaires were filled out at between 11 and 15 weeks and between 34 and 37 weeks gestation. Comparison of birth outcome between the three weight gain groups was made with ANOVA and Bonferroni post hoc tests. Dietary factors related to at least optimal and excessive weight gain during pregnancy were represented with logistic regression controlling for potential confounding. RESULTS: Of the women, 26% gained suboptimal and 34% excessive weight during pregnancy. Women in late pregnancy with at least optimal, compared with women with suboptimal, weight gain were eating more (OR = 3.32, confidence interval (CI)=1.81-6.09, P