PDS 73: Neurological effects, Johan Friso Foyer, Floor 1, August 26, 2019, 10:30 AM - 12:00 PM Background: Concern has been raised regarding the possible effects of mobile phone use on children’s health. The World Health Organization has emphasized the need for research into the possible effects of radiofrequency electromagnetic field (RF-EMF) in children. We examined the association between prenatal and postnatal exposure to mobile phones and behavioral problems in children. Method: Study subjects were 763 mother-child pairs from a prospective birth cohort, Mothers and Children’s Health (MOCEH) study. Mother’s mobile phone call frequency and duration were assessed at early pregnancy (≤20 weeks), 36 and 60 months of children’s age via questionnaire. Children’s neurodevelopment was assessed using the Korea-Child Behavior Checklist (K-CBCL) of Infant Development-Revised at 4, 5 and 6 years of age. The K-CBCL is consisted of total behavior problems, internalizing and externalizing problem. Logistic regression analysis was applied to groups classified by trajectory analysis showing neurodevelopmental patterns over time. Models were adjusted for residential area, child’s gender, maternal age at child birth, household income, alcohol intake and urinary cotinine level at 5 years of age. Results: There was a significantly increased risk of having a high externalizing problem score from 4 to 6 years of age, in relation to an increasing maximum of mother’s mobile phone call duration at 36 and 60 months of age after adjusted several confounding factors (p-trend = 0.02). There was no association between mother’s mobile phone use during pregnancy and children’s behavior problem. Conclusions: We found association between postnatal exposure to mobile phone use and child’s behavior problems. Acknowledgement: This work was supported by the ICT R&D program of MSIT/IITP. [2019-0-00102, A Study on Public Health and Safety in a Complex EMF Environment]