Objective The potential impact of environmental exposure to pyrethroid insecticides on child neurodevelopment has just started to receive attention, despite their widespread use. We investigated the associations between prenatal and childhood exposure to pyrethroid insecticides and behavioral skills in 6-year-olds. Methods The PELAGIE cohort enrolled 3,421 pregnant women from Brittany, France between 2002 and 2006. When their children turned six, 428 mothers were randomly selected for the

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... and 287 (67%) agreed to participate. Children's behavior was assessed using the Strengths and Difficulties Questionnaire (SDQ). Three subscales (prosocial behavior, internalizing disorders and externalizing disorders) were considered. Five pyrethroid metabolites were measured in maternal and child urine samples collected between 6 and 19 gestational weeks and at 6 years of age, respectively. Logistic regression and reverse-scale Cox regression models were used to estimate the associations between SDQ scores and urinary pyrethroid metabolite concentrations, adjusting for organophosphate metabolite concentrations and potential confounders. Results Increased prenatal cis-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylic acid (DCCA) concentrations were associated with internalizing difficulties (Cox p-value=0.05). For childhood 3-phenoxybenzoic acid (PBA) concentrations, a positive association was observed with externalizing difficulties (Cox p-value=0.04) and high odds ratios (ORs) were found for abnormal or borderline social behavior (OR=2.93, 95% CI: 1.27, 6.78, and OR=1.91, 95% CI: 0.80, 4.57, for the intermediate and highest metabolite categories, respectively). High childhood trans-DCCA concentrations were associated with reduced externalizing disorders (Cox p-value=0.03). Conclusions The present study suggests that exposure to certain pyrethroids, at environmental levels, may negatively affect neurobehavioral development by 6 years of age.