In the present study, 50 preschoolers were formally and independently classified using both the Diagnostic and Statistical Manual of Mental Disorders, fourth edition (DSM-IV) and third edition-revised (DSM-III-R) criteria for attention-deficit hyperactivity disorder (ADHD). The sample consisted of 25 preschoolers classified as having ADHD and 25 typically developing preschoolers for comparison; the sample was matched on gender, age, and socioeconomic status. All 50 preschoolers were without neurologic or neurodevelopmental disorders, oppositional defiant disorder, or language delay. There were four key findings: first, of the 25 preschoolers with ADHD, DSM-IV classification was as follows: hyperactive-impulsivity type (68%), combined type (28%), and inattentive type (4%). Second, the DSM-IV profiles showed that several symptoms were either infrequently endorsed by parents, reflecting limited applicability to preschoolers with ADHD, or frequently endorsed by parents of typically developing preschoolers, thus reducing their diagnostic value. Third, of the 25 preschoolers classified as having ADHD using DSM-IV criteria, 16% would not have been classified as having ADHD using the DSM-III-R criteria. The DSM-IV criteria therefore appear to be more lenient than the DSM-III-R criteria for this age group. Fourth, two symptoms that were not included in the DSM-IV, but were part of the DSM-III-R, were found to have clinical value for differentiating preschoolers with ADHD from their typically developing peers.