Objective: This study examined the bifactor models of ADHD in three groups: adolescents from the general community (n = 214), adults from the general community (n = 366), and a clinic sample (n = 245). Method: For the adolescent sample, mothers provided ratings of the ADHD symptoms, and their teachers provided ratings for Emotional Symptoms, Conduct Problems, Hyperactivity, Peer Problems, and Prosocial Behavior. For the adult sample, all adults completed self-ratings of the ADHD symptoms and measures for depression, anxiety, and stress. For the clinic-referred sample, mothers provided ratings of the ADHD symptoms, and they were diagnosed for ADHD, Conduct Disorder/Oppositional Defiant Disorder, anxiety disorders, and depression disorders. Results: The findings for all samples supported the bifactor model, and there were differences in the way the general and specific factors correlated with the external variables. Conclusion: The findings support the validity of the bifactor model. (J. of Att. Dis. 2013; XX(X) 1-XX).