Computerized EEG spectral analysis and topographic mapping were performed on 14 patients with Wilson's disease (WD) and 10 normal subjects of comparable ages. The predominant EEG changes in WD were diffuse but uneven topographic abnormalities with a decrease in alpha activity, an increase in theta and delta activities, and a low voltage background mainly in the alpha frequency band. Eleven patients (80%) had at least one of the above EEG changes. Furthermore, topographic mapping provided more clearly defined foci of slowing and epileptiform activity. Patients with cerebral white matter involvement, akinetic-rigid syndrome, dystonia, or psychiatric symptoms tended to have more abnormal EEGs. It is concluded that EEG changes in WD are common and the quantitative EEG analysis can increase the likelihood of detecting mild or even subtle EEG abnormalities in individual patients as well as in the patient group.