A study was made of the incidence of certain types of disease among Seventh-day Adventists, a religious group of special interest because they refrain from smoking and drinking. Epidermoid cancer of the lung, previously shown to be related to smoking, was 10 times less common among Seventh-day Adventists than among the general population, even among those Seventh-day Adventists living in the Los Angeles area where all are exposed to smog. Similarly, cancers of the mouth, larynx, and esophagus, previously shown to be related not only to smoking but also to heavy drinking, were at least 10 times less common among Seventh-day Adventist men than among men of the general population. All other types of cancer, with the exception of cancer of the bladder and cervix, occurred among Seventh-day Adventists with the same frequency as in the general population. The latter occurred slightly less than in the general population. Myocardial infarction in Seventh-day Adventist males was less frequent and occurred at a later age than among males in the general population; while the age distribution of the disease among the Seventh-day Adventist females was similar to that of females in the general population.