Objectives:This study had explored multidimensional factors affecting on intelligence level in Attention Deficit Hyperactivity Disorder, Combined Type(ADHD-C). Methods:Explored factors were composed of a severity of behavioral symptoms in ADHD-C(attention deficit, hyperactivity and impulsivity), probable comorbid disorders including learning disorder and other psychiatric disorders as affective disorder, and neuropsychological functions as non-executive functions and executive functions. 149 ADHD-C patients were selected, and all of factors were administrated before therapeutic medication under a guideline of IRB for a retrospective study. Results:Although level of intelligence in ADHD-C was similar to a theoretical distribution of traditional intelligence tests, each factor was explained variations of intelligence in ADHD-C, respectively. But, considering of all of factors, only concept formation ability and working memory ability in executive function, and verbal development problem related with learning disability were explained variations of intelligence level in ADHD-C. Conclusions:This result had replicated previous research results, but we suggested that each result of previous researches were depend on propose of researchers and had limitation of having problems in selecting of subjects in clinical setting and normal control groups, and not free to a conceptual hierarchy and broad umbrella concepts of executive function.