The purpose of this study was to investigate the dietary factors associated with characteristics of attention deficit hyperactivity disorder (ADHD) in upper-grade elementary school students. The study subjects were 397 students, and 52% of total study subjects were boys. The risk for developing ADHD was assessed by using a DSM-IV questionnaire. Boy's ADHD score was higher than that of girls (p<0.001). Subjects were divided into two groups according to the median of the ADHD score in boys and girls. The high ADHD score group showed higher frequency of skipping breakfast and a lower score for good dietary habits, as compared to the normal group. Further, the high ADHD score group showed higher frequency of processed food intake with lower frequency of vegetable intake, as compared to the normal group. These results suggest that undesirable eating habits and frequent intake of processed foods may be associated with higher risk of developing ADHD in elementary school students.