An analysis of data obtained from the National Ambulatory Medical Care Survey (NAMCS), 1990-1995, for children aged 5 through 18 years, was performed at Washington State University, to discern trends in the prevalence of US office-based visits for ADHD and for prescriptions of stimulant medications, including methylphenidate (MPH), for ADHD treatment. From approximately 1 million diagnosed cases in 1990, the prevalence of ADHD had increased 2.3-fold in 1995. In this period, the number of office visits for girls diagnosed with ADHD rose 3.9-fold; the mean age of patients with ADHD increased by more than 1 year, from 9.7 to 10.8; the percentage of all office visits resulting in a diagnosis of ADHD rose from 1.1% to 2.8%; and the population-adjusted rate of ADHD patients prescribed stimulants increased 2.9-fold (2.6-fold for MPH). 
COMMENT. A 2.3-fold increase in the prevalence of the ADHD diagnosis in children and 2.6-fold increase in MPH prescriptions in the period 1990-1995 are partially explained by the increase in diagnosis of the syndrome in girls and the increasing age of patients treated in the US. One third of ADHD cases diagnosed during childhood still meet the diagnostic criteria in adulthood, according to Swanson JM et al. . In some centers, medication is continued through adolescence into early adulthood, contributing to the reports of an increased prevalence rate. 
A 1995 survey of pediatric neurologists regarding usage of stimulant medication for ADHD showed that, in this specialty, treatment was continued for a mean of 3.5 years, with a range of 1 to 5 years. Of patients treated, 70% were 6-12 years of age, and only 20% were 13-18 years.