There are few reports of EEG findings in patients with multiple personalities. In our study, EEGs were visually scanned and frequency analyzed in two patients with multiple personalities and one control. Auditory and visual evoked responses were also obtained from one of the patients and the control. The visually scanned EEGs and the evoked responses demonstrated few differences among the various personalities in each patient, whereas the frequency analysis showed the greatest number of significant differences among the "personalities" in the control. These data suggest that EEG differences among personalities in a person with multiple personalities involve intensity of concentration, mood changes, degree of muscle tension, and duration of recording, rather than some inherent difference between the brains of persons with multiple personalities and those of normal persons.