Research on the overlap between attention-deficit/hyperactivity disorder (ADHD) and conduct disorder (CD) in males has provided useful information on the etiology, correlates, course, and nosology of this co-morbid condition. However, it is unclear how these results extend to females. Our aim was to examine the predictors, clinical characteristics, and functional outcome of CD in a sample of female youth with and without ADHD.

We conducted a blind, 5-year prospective longitudinal study of girls with (n=140) and without (n=122) ADHD, aged 6–18 years at baseline. At the 5-year follow-up, 123 (88%) and 112 (92%) of the ADHD and control children respectively were reassessed at a mean age of 16·7 years. Psychiatric disorders were assessed using blind structured diagnostic interviews.

Baseline ADHD was a significant risk factor for lifetime CD throughout childhood and adolescence [hazard ratio (HR) 5·8, 95% confidence interval (CI) 2·9–11·5, p<0·001]. Among ADHD girls, childhood-onset (<12 years) CD was predicted by paternal antisocial personality disorder (ASPD), while adolescent-onset CD (⩾12 years) was predicted by family conflict. In addition, lifetime CD significantly predicted academic, psychiatric and sexual behavior problems in girls with ADHD at follow-up.

ADHD is a significant risk factor for CD in girls. CD is associated with increased risk for academic, psychiatric and sexual behavior problems compared to ADHD girls without CD. Given that the therapeutic approaches indicated by ADHD and CD differ, these findings highlight the importance of improved efforts aimed at early identification and treatment of CD in girls with ADHD.