BackgroundPrevious research suggests a relationship between attention-deficit hyperactivity disorder (ADHD) and smoking, alcohol and illicit drug use, however most studies have focused on adolescents or young adults, or clinically ascertained samples.AimsTo analyse population-based data on the relationship between ADHD and at-risk health behaviours in adolescents and adults.MethodData were derived from a Statistics Canada population-based health survey. The association between the diagnosis of ADHD and smoking, alcohol use, and illicit drug use was examined.ResultsIndividuals with ADHD started smoking at a younger age. They consumed more alcoholic drinks on drinking days, and women with ADHD were more likely to engage in binge drinking. Women over the age of 25 and men with ADHD were more likely to meet alcohol-dependence lifetime criteria. People with ADHD were at a greater risk of drug misuse and dependence.ConclusionsPeople with ADHD are more likely to partake in at-risk behaviours.