OBJECTIVE: To investigate the impact of prenatal antidepressant exposure on behavioural problems in children at 7 years of age. DESIGN: Nationwide population-based study. SETTING: Danish National Birth Cohort. POPULATION: A cohort of 49 178 pregnant women recruited between 1996 and 2002. METHODS: Data obtained from computer-assisted telephone interviews twice during pregnancy were used to identify children born to: (i) depressed women who took antidepressants during pregnancy (n = 210); (ii) depressed women who did not take any antidepressants during pregnancy (n = 231); and (iii) healthy women who were not depressed (n = 48 737). Childhood behavioural problems at 7 years of age were examined using the validated Danish parent-report version of the Strengths and Difficulties Questionnaire (SDQ). MAIN OUTCOME MEASURES: SDQ scores. RESULTS: No associations were observed between prenatal antidepressant exposure and abnormal SDQ scores for overall problem behaviour (adjusted relative risk, aRR 1.00; 95% confidence interval, 95% CI 0.49-2.05), hyperactivity/inattention (aRR 0.99; 95% CI 0.56-1.75), or peer problems (aRR 1.04; 95% CI 0.57-1.91). Although prenatal antidepressant exposure appeared to be associated with abnormal SDQ scores on the subscales of emotional symptoms (aRR 1.68; 95% CI 1.18-2.38) and conduct problems (aRR 1.58; 95% CI 1.03-2.42), these associations were significantly attenuated following adjustment for antenatal mood status (aRR 1.20; 95% CI 0.85-1.70 and aRR 1.19; 95% CI 0.77 1.83, respectively). Untreated prenatal depression was associated with an increased risk of all behavioural outcomes evaluated, compared with unexposed children, with significant attenuation following adjustment for antenatal mood status. CONCLUSIONS: The results of this study suggest that independent of maternal illness, prenatal antidepressant exposure is not associated with an increased risk of behavioural problems in children at 7 years of age. TWEETABLE ABSTRACT: Prenatal antidepressant exposure is not associated with an increased risk of child behavioural problems.