A longitudinal, prospective, birth cohort design was used in an investigation of the association between maternal smoking during pregnancy and hyperactivity in 8-year-old children followed at the University Hospital of Oulu, Finland. Teachers assessed behavior by the Children’s Behavior Questionnaire (Rutter B2), using a total score of 9 or more to define hyperactivity. At age 8 follow-up, 9.5% of children were identified as hyperactive. Boys (14.2%, n=617) were more often hyperactive than girls (4.6%, n=191). Smoking during pregnancy was more common among mothers of hyperactive children (39.7%, n=318) than of nonhyperactive children (26.9%, n=2,052). Maternal smoking was associated with hyperactivity in a positive dose-response relationship, especially in children of young mothers with low social standing. Single-parent families had the highest proportion of affected children. After adjustment for sex, family structure, socioeconomic status, maternal age, and maternal alcohol use, the odds ratio for a positive association was 1.30; 1.08-1.58). 
COMMENT. Maternal smoking is a potential risk for abnormal brain development and subsequent diagnosis of behavioral disorders. Discontinuing use of nicotine during pregnancy should lessen the incidence of hyperactive behavior in young children.