Smoking rates are elevated among individuals with attention-deficit/hyperactivity disorder (ADHD). The association of ADHD diagnosis and smoking treatment outcome has not been examined. The present study examined abstinence rates among 428 adult smokers participating in two randomized controlled trials. Treatments included nicotine replacement, antidepressants, and psychological interventions. Childhood ADHD was assessed retrospectively by diagnostic interview. In a survival analysis, ADHD status predicted time to relapse after controlling for gender, history of depression, and baseline smoking variables. Only 1 of 47 participants with a history of childhood ADHD remained abstinent by week 52, compared with 18% of those who had no history of childhood ADHD (adjusted OR=0.36, 95% CI=0.28-0.45). The current findings provide preliminary evidence for an association between childhood ADHD and smoking cessation treatment failure. Further investigation is warranted.