The growth of specialization in the practice of medicine has reached a point where it may well be asked, first, whether the mortality of physicians so engaged differs from that of physicians in general practice and, second, what differences in mortality there may be among the several specialties. The answers to these questions may be determined from an analysis of the records used for an earlier study in which the mortality of all American physicians during the period 1938-1942 was compared with that of the general population.1 For the purposes of the present investigation, only physicians devoting full time to their specialty were considered as specialists, in accord with the following excerpt from the American Medical Directory (sixteenth edition, 1940): A symbol designating specialty practice is entered on request whenever the physician is (1) a member of a constituent state association, (2) a member of a special national or