on behalf of the EDEN Mother-Child Cohort Study Group (Etude des Déterminants pré-et postnatals précoces du développement et de la santé de l'Enfant)* Objective To examine the relationship of polyunsaturated fatty acid (PUFA) in breast milk with children's IQ. Study design In the French Etude des Déterminants pré-et postnatals précoces du développement et de la santé de l'Enfant (EDEN) mother-child cohort, colostrum samples were collected at the maternity unit. Colostrum omega-6 and omega-3 PUFA were analyzed by gas chromatography. At age 5-6 years, the IQs of 1080 children were assessed using the Wechsler Preschool and Primary Scale of Intelligence-III. The relationships of breastfeeding duration and PUFA levels with children's IQs were examined by linear regression. Results Full scale IQ of ever breastfed children was 4.5 (95% CI: 2.7, 6.2) higher than never breastfed children in the unadjusted model, but this was not statistically significant in the adjusted model (1.3 points higher [-0.4, 3.0]). Any breastfeeding duration was associated with full scale (0.20 [0.00, 0.41] points/month) and verbal [0.31 [0.09, 0.52]) IQ. Colostrum linoleic acid (LA) levels were negatively associated with Verbal IQ (-0.6 [-1.1, 0.0] points per 1% level increase). Children exposed to colostrum high in LA and low in docosahexaenoic acid (DHA) had lower IQs than those exposed to colostrum high in DHA (3.0 [0.5, 5.5] points) and those exposed to colostrum low in LA and DHA (4.4 [1.6, 7.3] points). Finally, the association between breastfeeding duration and child IQ was stronger when LA levels were high. Conclusions Duration of breastfeeding and colostrum PUFA levels were associated with children's IQs in the EDEN cohort. These data support breastfeeding and add evidence for the role of early PUFA exposure on childhood cognition. (J Pediatr 2017;■■:■■-■■).