ObjectiveTo use a single national data source to discern trends in the prevalence of office-based visits resulting in a diagnosis of attention deficit hyperactivity disorder (ADHD) among girls, and trends in the prescribing of stimulant pharmacotherapy (including methylphenidate) for its treatment in the US.MethodsData from the US National Ambulatory Medical Care Survey were utilised for this analysis. The number and rate of office-based physician visits resulting in a diagnosis of ADHD (International Classification of Diseases, 9th Revision, Clinical Modificationcode 314.00 or 314.01) were discerned from the beginning of 1990 to the end of 1998, for children aged 5 to 18 years. Gender-specific trend analyses were conducted using four time intervals: 1991 to 1992, 1993 to 1994, 1995 to 1996, and 1997 to 1998.ResultsThe estimated number of office-based visits documenting a diagnosis of ADHD among children increased from 947 208 in 1990 to 3 234 180 in 1998. The rate of office-based visits documenting a diagnosis of ADHD among children increased from 19.4 per 1000 of the US population aged 5 to 18 years in 1990 to 59.0 per 1000 in 1998, a 3-fold increase (p < 0.05). The annualised mean number of office-based visits documenting a diagnosis of ADHD among girls tripled between 1991 to 1992 and 1997 to 1998 (from 296 389 to 886 798), whereas the number for boys increased 2.2-fold (from 1 006 243 to 2 200 021). The US population-adjusted rate of office-based visits documenting a diagnosis of ADHD among girls increased 2.7-fold between 1991 to 1992 and 1997 to 1998 (from 12.3 per 1000 girls to 33.4 per 1000; p < 0.05), whereas the rate among boys doubled (from 39.5 per 1000 boys to 78.7 per 1000; p < 0.05). Documentation of a diagnosis of ADHD and the prescribing of stimulant pharmacotherapy increased 2.8-fold for girls, from 7.5 per 1000 girls in 1991 to 1992 to 21.1 per 1000 in 1997 to 1998 (p < 0.05), as compared with a 2.2-fold increase among boys (from 25.5 per 1000 boys to 57.0 per 1000; p < 0.05).ConclusionOver the time frame 1990 to 1998, the rate of ADHD as well as the prescribing of stimulant medications for its treatment increased significantly among children aged 5 to 18 years. Between 1991 to 1992 and 1997 to 1998, the increased rate of diagnosis of ADHD among girls contributed to the overall upward trend. The rapidly increasing rate of ADHD among girls, and the prolonged nature of the disorder, represent significant public health problems. There exists a need for additional research examining both the aetiology and treatment of ADHD by gender.