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Prenatal folic acid exposure has been linked to higher risk of childhood asthma in countries that do not fortify the food supply with folic acid. This study seeks to examine this association in the United States, where the food supply is generally fortified with folic acid. Participants were 1279 mother-child pairs from Project Viva, an ongoing prospective birth cohort, with folic acid intake in pregnancy assessed through validated food frequency questionnaires. The primary outcome was physician-diagnosed asthma at mid-childhood. In an unadjusted logistic regression model, higher folic acid intake was associated with lower odds of asthma in mid-childhood (odds ratio [OR] 0.48; 95% CI 0.31-0.76). However, in the adjusted analysis this association was attenuated (adjusted OR [aOR] 0.80; 95% CI 0.49-1.33). Our results suggest that in the United States, where there is generalized folic acid fortification of food, maternal folic acid intake during pregnancy is not associated with asthma development in offspring.