Context: The DSM-IV definition of attention-deficit/hyperactivity disorder (ADHD) distinguished 3 subtypes that had not been extensively studied.

Objective: To determine whether the ADHD subtypes are stable enough over time to be valid.

Design: Longitudinal study with a greater-than 89% retention rate in 7 assessments over 8 years.

Setting: Outpatient clinics.

Participants: Volunteer sample of 118 4- to 6-year-olds who met DSM-IV criteria for ADHD, including impairment in 2 settings in at least 1 assessment.

Main outcome measure: Meeting DSM-IV criteria for the subtypes of ADHD during years 2 through 8.

Results: The number of children who met criteria for ADHD declined over time, but most persisted. Children who met criteria for the combined subtype (CT, n = 83) met criteria for ADHD in more subsequent assessments than children in the predominantly hyperactive-impulsive subtype (HT, n = 23). Thirty-one (37%) of 83 CT children and 6 (50%) of 12 children in the predominantly inattentive subtype (IT) met criteria for a different subtype at least twice in the next 6 assessments. Children of the HT subtype were even more likely to shift to a different subtype over time, with HT children who persisted in ADHD mostly shifting to CT in later assessments. The subtypes exhibited consistently different mean levels of hyperactive-impulsive symptoms during years 2 through 8 that corresponded with their initial subtype classifications, but initial subtype differences in inattention symptoms diminished in later years.

Conclusions: In younger children, the CT and IT may be stable enough to segregate groups for research, but they seem too unstable for use in the clinical assessment of individual children. Children rarely remain in the HT classification over time; rather, they sometimes desist from ADHD but mostly shift to CT in later years. Using continuous ratings of hyperactivity-impulsivity symptoms as a diagnostic qualifier should be considered as an alternative to classifying nominal subtypes of ADHD in DSM-V.