Background: Attention deficit hyperactivity disorder (ADHD) is the most common mental disorder in the pediatric population and affects education, finances, and medication. ADHD diagnostic criteria and resultant prevalence rates are also of special interest to the global psychiatric community. ADHD diagnosis rates and the corresponding demographic distributions through different years are thus an issue of great public health concern and debate. The objective of this study is to characterize changes in the demographic distribution of ADHD diagnosis from 2004 to 2012 in the United States. Methods: ADHD diagnosis data was extracted from the National Health and Nutrition Examination Survey (NHANES) Summary Health Statistics for United States Children, a source of nationally representative data on children in the United States. The ADHD cases were identified based on ICD9-CM diagnosis codes. Chi-square tests were used to investigate differences in ADHD diagnosis rates by demographic characteristics (age, race, and gender) within each year and simple linear regression was applied to determine the extent of change over time. Results: The ADHD diagnosis rate was higher among males, whites, and school-aged children and adolescents (vs. preschoolers aged 3-4) in each year examined. The total number of ADHD cases as well as all demographic groups with the exception of African Americans and preschoolers aged 3-4 exhibited an increasing trend between 2004 and 2012. Conclusions: ADHD diagnosis among youth showed a significant increase in the United States between 2004 and 2012. Notable increases and group differences were also observed among demographic subgroups. These findings indicate a need for future research in reasons for such group differences as well as treatment differences.