The overall the cause-specific mortality experience of male radiologists and a comparable group of medical specialists, pathologists, who were included in the Radiation Registry of Physicians, is presented. The study population consists of an early-entry cohort of physicians who were members of either the American College of Radiology or the College of American Patholigists as of Jan 1, 1962, and a late-entry cohort of similar members who joined these societies between January 1962, and June 1972. The purpose of the study was to deterjine if occupational exposure to low levels of ionizing radiation resulted in excess mortality from al causes and specific causes, or decreased survival patterns or radiologists compard with patholigists over the 16-yuear period, 1962 to 1977. The data revealed that radiologists and pathologists were comprable regarding overall mortality experience for all entrants, the early-entry cohort, and the late-entry cohort. Further analyses revealed a gradient in mortality between the two specialties, with the largest differences in the earliest birth subcohorts for all three groups, and a significant excess in mortality among radilogists in those subcohorts of the late-entry cohort born before 1920. Such a gradient may indicate an exposure effect associated with time of entry into a professional society. Nevertheless, overall age-specific and age-adjusted mortality rates among radiologists and pathologists were lower in the late-entry cohort compared with the early-entry cohort, thus indicating some effect of the time of entry within each specialty. Although there were too few deaths to permit analysis of specific causes of death for the late-entry cohort, such analyses for all entrants, the early-entry cohort, and those born before 1920 revealed no significant differences regarding major causes of death between radiologists and pathologists. A marginal excess (P < .10) of circulatory diseases was noted among radiologists born before 1920. further analyses of specific systems revealed a significant excess of chronic lung disease among pathologists in the early-entry cohort and for those born before 1920.