The aim of this study was to identify dietary predictors of plasma dioxin-like activity in women from the Danish National Birth Cohort. Associations between exposure and birth weight and infant development at 6 months were also explored. Diet was assessed in mid-pregnancy by a food-frequency questionnaire. One hundred nulliparous 25-35-year-old women of normal pre-pregnancy body-mass-index were chosen according to their intake of fatty fish, as fatty fish is a potential route of exposure. Intake of other foods of animal origin was also explored. Dioxin-like activity was measured in plasma using the Dioxin-Responsive Chemically Activated LUciferase eXpression (DR-CALUX) and quantified in toxic equivalents (CALUX-TEQs). Information on infant attainment of specific milestones was obtained by maternal report in a standardized interview. The sample mean was 46 pg CALUX-TEQ/g lipid. Plasma dioxin-like activity increased by 10.7 pg CALUX-TEQ/g lipid (95% CI: 1.8; 19.7) for the highest compared to the lowest tertile of total dietary fat intake but decreased by -9.8 pg CALUX-TEQ/g lipid (95% CI: -19.4; -0.2) for fatty fish intake. The inverse association for fatty fish was explained by lower intake of high-fat food groups such as red meat, fats and oils, which were also predictors of dioxin-like activity. Plasma dioxin-like activity was not associated with birth weight, but an inverse correlation was observed with total developmental score (Spearman r=-0.23, p=0.046). Our study indicates that dietary patterns associated with high fat intake may lead to increased plasma dioxin-like activity and in utero exposure might be related to early infant development.