Discrimination of psychopaths from non-psychopaths wichin a prison secting can be advantageous boch in terms of segregating these groups for treatment and for research. The present study was an attempt to determine, by means of a check list of psychiatrically defined characteristics of psychopachs, which prisoners would be grouped under the category of psychopath and which would not. The underlying assumption was that . . all criminals are certainly not psychopachs (Pennington 8: Berg, 1954, p. 427). As a check on the validity of che selection, the two groups were compared by using the Minnesoca Multiphasic Personality Inventory (MMPI) since ocher scudies have indicated its usefulness in recognizing the psychopathic group (Dahlstrom & Welsh, 1960, p. 102; Gough, 1946; Guthrie, 1950; Hunt, et al., 1948; McKinley & Hathaway, 1944; Schmidt, 1945). A cwo-year follow up decermined the number of prisoners from each group known to return in that time period to some prison. METHOD From a pool of 126 characteristics obcained from the psychiatric literature, 56 items considered representative of the 126 were condensed into simple statements.Qch statement was numbered and presented in the form of a. check list to 10 Saskatchewan psychiatrists who were asked to race each item as very significant, significanc, or of little significance in diagnosing a psychopach. Of the 10 psychiatrists, 3 were selected who agreed on the mosc items (18) in their ratings, and all icems (with one excepcion) raced as very significant or significanc were included in a final check list. The one item deleted from the list, shows inadequate and ofcen aggressive behavior to society, was considered useless in differentiating between groups already incarcerated. Items on the check list indicaced in Table 1 were given arbitrary weightings of 1 and 2 depending upon their original rating as significanc or very sigp~ ~~ 'This study represents a reworking of a master's thesis completed at the University of Alberta, Edmonton, Alberta, and presented at MPA, Detroit, 1958. The author wishes to express his gratitude to D. Smith for his guidance throughout the study, and to D. Spearman for his suggestions and help in the development and use of a psychopathic check list. 'The original check list may be obtained for a fee from the American Documentation Institute. Order Document No. 7097 from AD1 Auxiliary Publications Project, Photoduplication Service, Library of Congress, Washingron 25, D.C., remitting in advance $1.25 for microfilm or photocopies. Make checks payable to: Chief, Photoduplication Service, Library of Congress.