The purpose of this study was to examine the ability of the Cognitive Assessment System (CAS) and the NEPSY, A Developmental Neuropsychological Assessment, to differentiate between the subtypes of Attention Deficit/ Hyperactivity Disorder (AD/HD). The CAS and NEPSY are neuropsychological instruments which provide norms for AD/HD children in general. This study examined the performance of the two subtypes of AD/HD on the CAS and NEPSY. In addition, this study examined the performance of the two AD/HD groups on the Screening Test for Auditory Processing Disorders (SCAN). Since AD/HD children tend to have difficulty with language, the SCAN was used to determine if any of the AD/HD subjects had auditory processing difficulties that might impact their performance on the CAS and/or NEPSY subtests. The sample consisted of 118 children between the ages of 8 and 12 years of age. Using the DSM-IV criteria, the children were diagnosed as having three types of AD/HD: A Predominantly Hyperactive-Impulsive Type (AD/HD-HI), a Predominantly Inattentive Type (AD/HD-I) and a Combined Type The subtypes were also identified by the Attention Deficit Disorders Evaluation Scale-Home Version (ADDES-H). Only two subtypes, AD/HD-I and AD/HD-C, were identified by the ADDES-H. There were not enough AD/HD-HI subjects to include in …