For the purpose of judging the importance of the question of feeble-mindedness among the most serious criminals, those committed to the state prison, we have a very important study by Rossy (_48_). Three hundred cases were taken at random with the exception of a few selected cases on which a report was requested. In this group, thirty prisoners could not be examined either because of language difficulties or because of their refusal to be tested. The Point Scale of Yerkes and Bridges was used and the results are presented in terms of mental ages on that scale. The examiner considered all those testing XI or under as feeble-minded and found 22% of the 300 in this class. This is less conservative than even our doubtful standard, but I estimate that 16% would fall within our doubtful and presumably deficient groups. This includes 11% who test X or under with the Point Scale plus 54% of those who tested XI. This estimate is made on the basis of the tables given by Haines (_26_), comparing Binet 1911 results with those of the Point Scale on the same individuals. It adds the proportion of those testing XI with Point Scale, who would test nearer X with the Binet 1911 scale. Ordahl[21] examined 51 convicts in the penitentiary at Joliet, Ill. They “were selected in a manner thought to secure fair representation of the prison population as a whole.” The Kuhlmann 1911 Binet scale was used and supplemented by tests for 13 to 18 years taken from the Stanford scale. It is possible that selection affected the results with this small group, since 25% showed test ages of IX or under and 36% tested X or under. Haines tested with the Point Scale 87 consecutive admissions to the Ohio penitentiary (_24_). He found 18% tested below a record corresponding to X.6 on the Goddard 1911 scale, which is about the upper limit of our doubtful group. That a smaller proportion of the state prison inmates is found intellectually deficient than is found among the inmates of the industrial schools is not surprising. This may be due to various causes. Among these may be mentioned the failure to recognize feeble-mindedness, heretofore, among the younger delinquents while the adult feeble-minded were more carefully isolated in their proper institutions. The deficient adults have also been reduced in frequency by the excessive mortality. Probably the feeble-minded are not so likely to plan or commit felony as lesser crimes and misdemeanors. Moreover the adult feeble-minded may be more stable and less inclined to delinquency than adolescents. Whatever may be the explanation, deficiency generally does not seem to be as common among the inmates of a state prison as among minor delinquents in states which are in the forefront in the care of their feeble-minded.