Abstract– Sixty-one boys, 6–12 years old, met both the diagnostic criteria of ADHD of DSM-III-R and hyperkinetic syndrome of ICD-9. They could be subdivided into two groups: 43 showed hyperactive symptoms in the clinic situation and 18 did not. The former group were younger and showed significantly poorer performance in measures of general intelligence, attention, cognitive styles, motor clumsiness and minor neurological deficits. Controlling for age and intelligence attenuated the differences, but significant differences remained in activity level, attention, and minor neurological deficits. This result suggests that direct observation is important in the assessment of pervasiveness of childhood hyperactivity.