Objectives: This study was performed to assess the comorbidity and associated emotional and behavioral manifestations in attention deficit hyperactivity disorder(ADHD) subjects, and the parenting stress and sense of competence in their mothers. Method: To investigate the comorbid conditions of ADHD, 102 ADHD patients(82 males, 9.58±2.65) and their caregivers visiting outpatient clinic were interviewed using the Korean version of Kiddie-Schedule for Affective Disorders and Schizophrenia-Present and Lifetime. The Korean-Child Behavior Checklist, Children`s Depression Inventory, and Revised Children`s Manifest Anxiety Scale(RCMAS) were used to measure the psychopathologies in the subjects. The Parenting Stress Index/Short form and Parenting Sense of Competence Scale were also applied to the caregivers of ADHD patients. Results: Eighty-four(82.4%) of ADHD subjects had comordid psychiatric disorders. Comorbid oppositional defiant disorder, anxiety disorders, tic disorders, and elimination disorders were accompanied with ADHD in 54.9%, 24.9%, 19.6%, and 12.7%, respectively. Mean scores of Social Problems, Total Behavior Problems, and RCMAS were significantly higher in comorbid ADHD group than pure ADHD group. Parents of ADHD patients with comorbidity reported higher parenting stress and lower parenting sense of competence. Conclusion: Majority of ADHD patients had comorbid psychiatric conditions, and more psychopathologies and related parenting complications were associated with comorbidity.