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AIM: To study the association between intrauterine exposure to tobacco smoke and behavioural disorders in preschool children, primarily symptoms of inattention, hyperactivity and impulsivity but also hostile-aggressive and anxious-fearful symptoms. METHODS: We conducted a follow-up study in 1355 singletons born to Danish-speaking mothers. Information on smoking habits during pregnancy and other lifestyle factors was obtained from self-administered questionnaires filled in during second and third trimester. Approximately 3.5 years later, the parents provided information on their child's behaviour using the self-administered Preschool Behaviour Questionnaire. The children were categorized into three not mutually exclusive behaviour groups: hyperactive - distractible (13.6%), hostile-aggressive (4.6%), and anxious-fearful (6.4%) children. RESULTS: Compared with children of non-smokers, children born to women who smoked 10 or more cigarettes per day had a 60% increased risk of hyperactivity and distractibility perceived by the parents (OR 1.6; 95% CI 1.0-2.3; P < 0.05). The results were adjusted for maternal lifestyle factors and socioeconomic characteristics. Additional adjustment for perinatal factors and parental psychiatric hospitalization did not change the results substantially (OR 1.7; 95% CI 1.1-2.6). We found no statistically significant association between maternal smoking in pregnancy and hostile-aggressive and anxious-fearful behaviour in the offspring. CONCLUSION: Exposure to tobacco smoke in utero was associated with hyperactive-distractible behaviour in preschool children.