The tendency to view certain types of criminals as neuropsychiatric problems brings into focus the importance of a consideration of abnormalities of the central nervous system, as well as psychogenic factors. Electroencephalography seems to be an effective method of detecting many such abnormalities. The purpose of this communication is to report and interpret the electroencephalographic observations on 411 male criminals at the Medical Center for Federal Prisoners. MATERIAL AND METHODS Criminologic and sociologic data on the prisoners are given in tables 1, 2 and 3, and their residential distribution is shown in figure 1. Clinically, the prisoners were classified under four large categories: psychopathic states (208 men), psychoses (80 men), normal mental status (60 men) and abnormalities of the central nervous system (63 men). The last group was included solely as a check on the competence of the technic employed in detecting abnormalities of the brain by the electroencephalogram; the