In a 10-year follow-up study electroencephalograms (EEGs) of 31 hyperactive and 27 matched control subjects of mean ages 19.17 and 18.59 years respectively showed no significant differences in any of the features assessed. Sequential EEGs, available for only the hyperactive subjects, suggested that a much greater proportion were normal at the 10-year follow-up assessment than at the 5-year follow-up assessment and that the normalization tended to take place mainly in the second 5-year period. This supports the hypothesis that EEG abnormalities of hyperactive persons are those of an immature pattern that tends to normalize with age. Correlation between EEG findings at the 10-year follow-up assessment and global outcome measures was not significant. Initial and 5-year EEGs also failed to predict global outcome at the 10-year follow-up assessment.