OBJECTIVES: To examine the economic burden and health care utilization of attention deficit/hyperactivity disorder (ADHD) in the US Medicaid population. METHODS: A case-control study was performed using US national Medicaid claims from 01JAN2008 through 31DEC2010. ADHD patients were identified using the International Classification of Diseases, 9^th Revision, Clinical Modification diagnosis code: 314.01 from 01JAN2009 to 31DEC2009. The diagnosis date was designated as the index date. A control cohort of patients without an ADHD diagnosis was matched 1:1 with the case cohort of ADHD patients having the same age, region, gender, and index year. A random index date was chosen for the control cohort to reduce selection bias. Patients were required to have continuous health plan enrollment for at least 12 months pre- and post-index date. One-to-one propensity score matching (PSM) was performed to compare follow-up health care costs and utilizations between the two cohorts, adjusting for demographic characteristics and the baseline Charlson Comorbidity Index (CCI) score. RESULTS: Eligible patients (N=98,965) were identified and included in each cohort. Compared with controls, ADHD patients tended to have higher CCI scores (0.42 vs. 0.31, p<0.0001), and a higher proportion of comorbidities, such as congestive chronic pulmonary disease (13.97% vs. 9.79%), and depression (10.73% vs. 3.42%, p<0.0001). After 1:1 PSM, 83,899 patients were matched, and the cohorts were well-balanced. A higher percentage of ADHD patients had health care utilization, including inpatient (6.85% vs. 3.64%), long-term care (LTC) (5.38% vs. 1.34%), pharmacy (94.70% vs. 63.27%), and outpatient visits (99.79% vs. 83.26%; p<0.0001) than non-ADHD patients. Patients diagnosed with ADHD also incurred significantly higher costs, including LTC ($2,325 vs. $1,169), pharmacy ($3,061 vs. $1,272), outpatient ($9,384 vs. $6,368), ER ($113 vs. $73), and total health care costs ($15,500 vs. $9,498; p<0.0001). CONCLUSIONS: ADHD patients had a higher burden of illness compared to non-ADHD patients.