OBJECTIVES: To estimate the prevalence of diagnosis of attention-deficit/hyperactivity disorder (ADHD) and use of stimulants for children aged 3-18 years in the US ambulatory settings. METHODS: Data from the National Ambulatory Medical Care Survey (NAMCS) and the National Hospital Ambulatory Medical Care Survey (NHAMCS) 1993-2003 were used. The main outcome measures were annual visits with diagnosis of ADHD, visits with prescription of stimulants, and proportion of stimulants prescribed in visits with diagnosis of ADHD. Diagnosis of ADHD was determined using ICD-9-CM code 314. Stimulants (methylphenidate, dexmethylphenidate, pemoline, and amphetamine compounds) were identified by generic codes. 95% confidence intervals were calculated and PROC SURVEYFREQ in SAS 9.1 was used to account for the complex sampling designs of these surveys. The results were weighted to reflect national estimates. RESULTS: Outpatient visits made by children 3-18 years of age increased from 131 (95% CI: 109-153) million in 1993 to 165 (137-192) million in 2003. Diagnosis of ADHD increased 127%, from 3.2 (1.3-5.2) million to 7.4 (5.2-9.5) million, accounted for 2.5% (1.0%-3.9%) and 4.5% (3.4%-5.6%) of all visits made by children in 1993 and 2003, respectively. Visits with stimulants prescribed jumped from 2.7 (0.9-4.5) million in 1993 to 6.6 (4.5-8.7) million in 2003. Proportion of stimulant use in children doubled over this period, from 2.1% (0.7%-3.4%) to 4.0% (3.0%-5.0%). Proportion of children with ADHD treated with stimulants ranged from 64.0% in 1997 to 77.3% in 1996, with an average of 70.4% (68.1%-72.8%) over the years studied. CONCLUSIONS: There was a steady growth in prevalence of ADHD and stimulant use among children aged 3-18 years in the US between 1993 and 2003. Approximately 70% children with ADHD were treated with stimulants. As appropriateness of treatment could not be determined in the current databases, whether this percentage represents overutilization of underutilization of stimulants merits further studies.