Although prenatal maternal smoking is an established risk factor for offspring's attention deficit hyperactivity disorder (ADHD), the studies of association between paternal smoking and childhood ADHD have produced inconsistent results.

The objective of the present study was to determine whether paternal smoking during early developmental period is associated with an increased risk of offspring's ADHD.

We conducted hospital-based case-control study with 107 medically diagnosed ADHD cases and 205 controls (aged 6–12 years). The diagnoses of ADHD were assessed with DSM-IV based semi-structured diagnostic interviews. Paternal smoking behavior was assessed with spouse-report questionnaire. The association between exposure to paternal smoking and ADHD were analyzed using multivariate logistic regression analysis. The primary outcome of interest was an odds ratio (ORs) reflecting the risk of offspring's ADHD incidence associated with father's smoking during the index pregnancy, up to one year after birth, and current smoking status. Control variables in our regression model were age, sex, financial status, parents’ education levels, low birth weight, and premature birth.

Our final regression model revealed that paternal smoking during pregnancy (OR = 1.68, 95% CI = 1.03–2.76) and up to one year after birth (OR = 1.69, 95% CI = 1.04–2.77) were significantly related to their offspring's ADHD.

The current results suggest that exposure to paternal smoking during the fetal and newborn period is associated with increased risk of ADHD. This study warrants public health policies to reduce children's exposure to secondhand smoke and their risk of ADHD.

The authors have not supplied their declaration of competing interest.