The comorbidity of ADHD in the general population of Swedish school-age children

This study examined patterns of comorbid/associated diagnoses and associate d problems in a population sample of children with and without DSM-III-R at tention-deficit hyperactivity disorder (ADHD). Half(N = 409) of a mainstrea m school population of Swedish 7-year-olds were clinically examined, and pa rents and teachers were interviewed and completed questionnaires. The child ren were followed up 2-4 years later. Eighty-seven per cent of children mee ting full criteria for ADHD (N = 15) had one or more - and 67% at least two - comorbid diagnoses. The most common comorbidities were oppositional defi ant disorder and developmental coordination disorder. Children with subthre shold ADHD (N = 42) also had very high rates of comorbid diagnoses (71% and 36%), whereas those without ADHD (N = 352) had much lower rates (17% and 3 %). The rate of associated school adjustment, learning, and behaviour probl ems at follow-up was very high in the ADHD groups. We concluded that pure A DHD is rare even in a general population sample. Thus, studies reporting on ADHD cases without comorbidity probably refer to highly atypical samples. By and large, such studies cannot inform rational clinical decisions.