Objective: To examine the relationship between smoking behaviour, mental disorders and emotional and behavioural problems in a nationally representative sample of young people. Method: Data were taken from the child and adolescent component of the National Survey of Mental Health and Wellbeing which assessed mental health problems in two main ways: using a fully structured interview (the Diagnostic Interview Schedule for Children) and using the Child Behaviour Checklist and the Youth Self Report, which assess emotional and behavioural problems on a dimensional scale. The relationship between smoking and mental health problems was assessed using logistic regression. Results: Among young people with conduct disorder 72% had smoked in the last 30 days, 46% of young people with depressive disorder, and 38% among young people with attention deficit hyperactivity disorder. This compared with 21% of young people with none of these disorders. Odds ratios (OR) for current smoking were consistently elevated for young people with mental health problems after adjusting for demographic and socio-economic factors across all measures of mental health used. The OR for current smoking in young people with parent-reported externalizing behaviours in the clinical range was 4.5 (95%CI: 3.16.8), and for young people with parent-reported internalizing problems in the clinical range the OR was 2.7 (95%CI: 1.84.0). Young people with mental health problems started smoking on average at a younger age, were more likely to progress to current smoking, and smoked on average a higher number of cigarettes per day. Conclusions: After adjusting for demographic and socio-economic factors, young people with mental health problems were more likely to start smoking, progress to daily smoking, and smoke more heavily. Mental illness is an important issue to consider in tobacco control in young people.