The concept of the psychopathic personality, long a controversial subject in psychiatry, has been greatly clarified in the recent literature. However, there are still disagreement about the delineation of the nosologic group and wide divergence of opinion about the essential psychopathology of the disorder. My object in this investigation was to study the etiologic factors, both organic and psychogenic, which were operative in a selected group of "typical" psychopaths, after I had arrived at a working definition of psychopathy which would be clinically distinct and homogeneous (though the disturbances of the various patients might vary greatly). As far as could be determined, this is the first application of electroencephalography to the study of adult psychopaths. In selection of the subjects no attention was paid to possible psychodynamic factors unless the resulting clinical state suggested neurosis or psychosis, in which case the patient was excluded from the investigation. Likewise, persons who