A new UCLA study shows that only about half of children diagnosed with attention-deficit hyperactivity disorder, or ADHD, exhibit the cognitive defects commonly associated with the condition. The study also found that in populations where medication is rarely prescribed to treat ADHD, the prevalence and symptoms of the disorder are roughly equivalent to populations in which medication is widely used. The results of the first large, longitudinal study of adolescents and ADHD, conducted among the population of northern Finland, appeared in several papers in a special section of the Journal of the American Academy of Child and Adolescent Psychiatry published in December and are currently online. ADHD is a common, chronic behavioral disorder characterized by inattention, hyperactivity and impulsivity that is thought to affect some 5 to 10 percent of school-age children worldwide. In adolescence, ADHD is generally associated with cognitive deficits, particularly with working memory and inhibition, which have been linked to overall intelligence and academic achievement, according to UCLA psychiatry professor Susan Smalley, who headed the research. Interestingly, the study showed that these deficits are only present in about half of adolescents diagnosed with ADHD.