Objective: Identification of differences among children with ADHD only, autism spectrum disorder (ASD)+ADHD, and chronic multiple tic disorder (CMTD)+ADHD may lead to better understanding of clinical phenotypes. Method: Children were evaluated using the parent- and teacher-completed questionnaires. Results: All three groups were highly similar in severity of oppositional defiant disorder and conduct disorder symptoms; however, the ASD+ADHD group generally exhibited the most severe anxiety, although the CMTD+ADHD group had the most severe generalized anxiety. The two comorbid groups had the most involved medical histories and the greatest likelihood of a family history of psychopathology. Conclusion: Groups differed in clinically meaningful ways, and the apparent association between tics and anxiety may explain in part the elevated levels of anxiety in both comorbid groups. Collectively, results suggest that ADHD may be better conceptualized as a family of interrelated syndromes defined in part by comorbid conditions and that continued research is clearly warranted. (Contains 5 tables.)