Objectives : It is known that adolescents with autism spectrum disorder (ASD) often concurrently exhibit attention-deficit hyperactivity disorder (ADHD). The objective of this study is to investigate how ADHD symptoms modify clinical characteristics in adolescents with ASD. Methods : Subjects were recruited from the Program for the Education Enrichment of Relational Skills program, which is a program for adolescents with ASD to promote and train social skills. The study participants and their parents completed the study questionnaires, such as the ADHD rating scale, Autism Diagnostic Observation Schedule, and Korean version of Child Behavior Checklist. Results : Adolescents with ASD and ADHD (N=19) were found to have more impaired sociality, less open communication with their parents, and more behavioral and emotional problems compared with adolescents with ASD, and without ADHD (N=28). Conclusion : Although further research is needed, the results of our study suggest that adolescents with ASD present different clinical characteristics when comorbid with ADHD.