• Attention deficit/hyperactivity disorder;
  • age of onset;
  • twin study;
  • follow-up study;
  • disruptive behavior disorders

Background:  To test whether the retrospective reporting of the age of onset impairment criterion for attention deficit/hyperactivity disorder (ADHD) required in the Diagnostic and Statistical Manual of Mental Disorders – IV (DSM-IV) complicates identification of new and known child and adolescent cases later in life.

Methods:  A birth-records-based cohort of twins assessed at ages 7 to 19 years were blindly reassessed five years later using the MAGIC interview. Study outcome measures were differences in reported ages of onset for attention deficit/hyperactivity disorder (ADHD), oppositional defiant disorder (ODD), conduct disorder (CD) and major depressive disorder (MDD).

Results:  For all age groups and respondents (parent on youth or youth self-report), later ages of ADHD onset were reported five years later. The same phenomenon was also present for the other diagnostic groups. Of the initial ADHD individuals who continued to meet all other ADHD criteria at follow-up, 46% failed the age of onset criterion five years later. When ignoring the age of onset criterion, late onsets of ages 7–16 years accounted for about 10% of all ADHD.

Conclusions:  Use of the DSM-IV age of onset criterion for attention deficit/hyperactivity disorder in the assessment of adolescents and young adults results in under-identification of affected individuals. Consideration should be given to revising the current nomenclatures to reflect the reality of retrospective reporting errors in age of onset as well as the presence of late onset cases.