Introduction Childhood attention deficit hyperactivity disorder (ADHD) is a common problem in developed countries like the UK.

Objective To determine the magnitude of the epidemiological association of pregnancy smoking with childhood ADHD.

Methods A retrospective cross-sectional survey was conducted in 2006 using a standardised respiratory health survey instrument to determine the association of ADHD risk with maternal smoking during pregnancy and childhood asthma prevalence. A total of 1074 schoolchildren aged 5–11 years in Merseyside were enrolled using a parent-completed questionnaire, and ADHD was defined by the question “does your child have attention deficit hyperactivity disorder (ADHD), which has been diagnosed by a doctor?”

Results The prevalence of maternal smoking during pregnancy, doctor diagnosed asthma and childhood ADHD was 28.0% (267/955), 19.4% (184/949) and 3.4% (32/945), respectively. The prevalence of ADHD was 5.6% (14/251) in children born to mothers who smoked during pregnancy (relative risk (RR) 2.44, 95% CI 1.1 to 4.9, p = 0.02) and 6.5% (11/170) in children with doctor-diagnosed asthma (RR 2.45, 95% CI 1.2 to 5.1, p = 0.01). Regression analysis adjusting for household socioeconomic status, low birth weight and child age showed a significant association of the risk of childhood ADHD with pregnancy smoking (adjusted odds ratio (AOR) 2.58, 95% CI 1.08 to 6.14, p = 0.05) and combined childhood asthma and maternal smoking during pregnancy (AOR 6.15, 95% CI 1.9 to 19.8, p = 0.002).

Conclusion Maternal smoking during pregnancy and childhood asthma are associated with the development of ADHD in childhood. These characteristics should be more widely recognised as markers associated with childhood ADHD. The biological mechanisms underlying the association with pregnancy smoking and ADHD require further study and early treatment of the underlying problem might improve the scholastic ability of these children.