Although young children with conduct disorder (CD) are suspected of having verbal and executive function deficits, most studies that investigated this hypothesis did not control for attention deficit hyperactivity disorder (ADHD). Furthermore, relatively little is known about the interaction between cognitive deficits and familial factors in explaining the onset and persistence of CD in children. The participants in this study were 57 children with CD and 35 controls aged 7 to 12 years. At 1-year follow-up, 41 of the participants with CD were reassessed. Children with CD were found to be significantly impaired in four of five executive function measures after ADHD symptoms and socioeconomic status (SES) were controlled. Executive function test performance, number of ADHD symptoms, and familial characteristics (SES, parental punishment) together correctly classified 90% of the participants. Only the number of ADHD symptoms was found to significantly improve prediction of CD 1 year later beyond that afforded by number of CD symptoms a year earlier. Findings indicate that children with CD and ADHD symptoms are especially at risk for persistent antisocial behaviour. Results also highlight the importance of treatment programs that cover both cognitive and familial aspects associated with CD.