Objectives : This study was conducted to examine whether there are qualitative differences in attention problem among children with various psychiatric disorders, including attention-deficit hyperactivity disorder (ADHD), depressive disorder, anxiety disorder, and tic disorder using clinical ADHD diagnostic system (ADS) T-scores. Methods : The subjects were 794 outpatient children aged from 5 to 15 years, including 540 children with ADHD, 95 children with depressive disorder, 86 children with anxiety disorder, and 73 children with tic disorder. Clinical T-scores on the ADS were calculated using the mean and standard deviations of four ADS variables for the ADHD group. Results : All four groups had T-scores on the ADS in the abnormal range. However, when comparing the clinical T-scores, the children with depressive and anxiety disorders performed better than the children with ADHD. We also found that although the four groups seemed to be similar in terms of clinical T-scores for omission and commission errors, there were significant differences in clinical T-scores for reaction time and the standard deviation of response time (RT) between the ADHD and other groups. Conclusions : We concluded that inattention and impulsivity might not be specific only to ADHD and that the clinical T-scores of RT and standard deviation of RT on the ADS could be used to discriminate between ADHD and other clinical groups.