OBJECTIVES: The aim of this research was to evaluate patient characteristics, length of stay (LOS), and costs among children and adolescents hospitalized in the United States (US) for ADHD.  METHODS: The study used data from 2000-2006 in the Healthcare Cost and Utilization Project Nationwide Inpatient Sample (HCUP-NIS). Patients included were children (6-11 years old) and adolescents (12-17 years old) that were hospitalized with a primary diagnosis of ADHD (ICD-9-CM 314.00 or 314.01). Data collected includes age, gender, race, payer type, admission source, admission type, geographic region, hospital status, year admitted, mean LOS and mean costs.  RESULTS: Among children, 28,247 patients met inclusion criteria and 83.74% were male. Medicaid was the most common form of health insurance (68.97%) followed by private insurance (26.67%). The majority of patients were hospitalized in urban locations (96.69%) and were admitted from the emergency room (33.75%). Mean (SE) LOS was 10.76 days (0.85) and mean (SE) costs were $10,106 ($1,358). Among adolescents, 21,612 patients met inclusion criteria and 75.70% were male. Medicaid was the most common form of health insurance (57.38%) followed by private insurance (36.99%). The majority of patients were hospitalized in urban locations (93.83%) and admitted from the emergency room (38.77%). Mean (SE) LOS was 8.66 days (0.66) and mean (SE) costs were $7886 ($1387). The number of hospitalizations for ADHD in each individual year from 2000-2006 was fairly constant for both children and adolescents.  CONCLUSIONS: Children and adolescents hospitalized for ADHD carry a substantial economic burden to the US health care system. The majority of these patients are male, come from urban locations and have Medicaid as their primary form of health insurance. Health care decision makers should be aware of the burden of ADHD in these populations. Research evaluating the impact of behavioural and/or pharmalogical ADHD treatment on hospitalizations should be explored.