Objective: To compare psychiatric comorbidity between the three symptom subtypes of Attention-Deficit/Hyperactivity Disorder (ADHD), Inattentive (I), Hyperactive-Impulsive (H), and Combined (C), in adults. Method: A clinic sample (N = 487) and a nonreferred community sample (N = 900) completed a DSM-IV-referenced rating scale and a questionnaire (social, educational, occupational, and treatment variables). Participants were assigned to one of four groups: ADHD:I, ADHD:H, ADHD:C, and NONE. Results: All three ADHD symptom groups reported more severe comorbid symptoms than the NONE group; the ADHD:C and NONE groups were the most and least severe, respectively; and there were clear differences between the ADHD:I and ADHD:H groups. The pattern of group differences was similar in both samples. Conclusion: ADHD symptom subtypes in adults are associated with distinct clinical correlates. The diversity of self-reported psychopathology in adults who meet symptom criteria for ADHD highlights the importance of conducting broad-based evaluations. (Contains 3 tables.)