ADHD is a common disorder in young people and smoking is a common comorbidity for young people with ADHD. Is the link purely behavioural or is there a heritable link? Geeta Thakur (Arch Dis Child2012;97:1027-1033 doi:10.1136/archdischild-2012-301882) and colleagues from Montreal share their findings that there may be an identifiable heritable factor which increases the risk for ADHD and smoking behaviour through a common mechanism, possibly externalising behaviours and specific cognitive deficits that manifest as ADHD in childhood and are the gateway to smoking behaviour later in life. In an accompanying editorial (Arch Dis Child2012;97:1011-1012 doi:10.1136/archdischild-2012-302461) Miriam Cooper and Anita Thapar report that the study represents "an intriguing starting point from which to conduct further related analyses. Acknowledging that the same genetic risk variants can have different phenotypic effects could help inform discovery of risk variants for childhood developmental/psychiatric disorders for which it can be difficult to assemble very large sample sizes"