ABSTRACT. Research literature relating to the prevalence of attention-deficit/hyperactivity disorder (ADHD) and co-occurring conditions in children from primary care settings and the general population is reviewed as the basis of the American Academy of Pediatrics clinical practice guideline for the assessment and diagnosis of ADHD. Epidemiologic studies revealed prevalence rates generally ranging from 4% to 12% in the general population of 6 to 12 year olds. Similar or slightly lower rates of ADHD were revealed in pediatric primary care settings. Other behavioral, emotional, and learning problems significantly co-occurred with ADHD. Also reviewed were rating scales and medical tests that could be employed in evaluating ADHD. The utility of using both parent-and teacher-completed rating scales that specifically assess symptoms of ADHD in the diagnostic process was supported. Recommendations were made regarding the assessment of children with suspected ADHD in the pediatric primary care setting. Pediatrics 2001;107(3). URL: http://www.pediatrics.org/cgi/content/ full/107/3/e43; prevalence, attention-deficit/hyperactivity disorder, primary care.ABBREVIATIONS. ADHD, attention-deficit/hyperactivity disorder; TRI, Technical Resources International; DSM, Diagnostic and Statistical Manual; DISC, Diagnostic Interview Schedule for Children; EEG, electroencephalogram; ERP, event-related potential.A ttention-deficit/hyperactivity disorder (ADHD) has defining features of inattention, overactivity, and impulsivity. 1 It is the most frequently encountered childhood-onset neurodevelopmental disorder in primary care settings. Symptoms frequently co-occur with other emotional, behavioral, and learning problems, including oppositional defiant disorder, conduct disorder, depression, anxiety, and learning disabilities. The cause of ADHD is unknown, and multiple pathways may lead to the phenotypic expression of the disorder. 2 Public awareness of ADHD has increased, and the disorder represents a public health concern with significant effects on children's functioning across multiple areas. 2 Referrals to health care professionals for children suspected of having the disorder continue at a high rate, and changes in the health care system in the United States have placed increasing demands on primary care pediatricians to diagnose and manage the disorder. It is now recognized that ADHD is a chronic condition that will persist over the life span. 2 The American Academy of Pediatrics Committee on Quality Improvement Subcommittee on Attention-Deficit/Hyperactivity Disorder synthesized a clinical practice guideline for the diagnosis and evaluation of children with ADHD. 3 This report will highlight the empirical literature review on which this practice guideline is based. The subcommittee worked with Technical Resources International (TRI), Washington, DC, under the auspices of the Agency for Healthcare Research and Quality, to develop an evidence base addressing questions regarding the prevalence, co-occurring conditions, and diagnostic ...