Symptomatology and electroencephalographic abnormalities were examined in thirty-nine individuals with borderline personality disorder, compared with twenty unipolar depressed patients. Borderline individuals showed a much higher incidence of symptoms commonly seen in complex partial seizures or episodic dyscontrol, and in addition had a much higher incidence of EEG abnormalities, particularly posterior sharp activity. These findings suggest that neurophysiological dysfunction may contribute to the borderline syndrome.