Conduct disorder is a heterogenous disorder of various etiology affecting 4-10% of school-age children. There is suggestive evidence that the comorbid group of conduct disorder and attention deficit hyperactivity disorder is different from these two separated diseases groups. There findings suggest that this comorbid group may present a meaningful subgroup. This study is conducted to examine the content validity of hyperkinetic conduct disorder that accepted first in International Classification of Disease 10th edition. The results are summarized as follows : 1) Using Conners Parenting Rating Scale, Parent Rating Scale Form for DSM-III-R, the mean scores of attention deficit hyperactivity disorder in conduct disorder were significantly higher compared with those of normal controls. 2) 72.4% of conduct disorder and 41.5% of normal control groups showed simultaneous attention deficit hyperactivity disorder. The diffenence between conduct disorder and normal control groups was significant. There were many previous informations that children with attention deficit hyperactivity disorder had conduct disorder as comorbid disorder and these result show that children with conduct disorder also significantly had attention attention deficit hyperactivity disorder reversibly. Then these show that hyperkinetic conduct disorder-diagnosis used when both the overall criteria for hyperkinetic disorders and the overall criteria for conduct disorders are met-have satisfactory content validity. Biological, familial or long term studies are needed to further validate this diagnostic category.