This study document the wide-ranging significance for the health of the person's sense of control, i.e., the sense of mastery vs. fate-orientation. Health behavior is examined in three domains: 1) preventive care; 2) health knowledge and perspectives; and 3) physical status, e.g. acute and chronic illness. A representative metropolitan sample was interviewed at the beginning (1976) and at the close (1977) of a year-long investigation that included telephone call-backs at six-week intervals to trace health-related incidents. Data collection consisted of initial and final face-to-face interviews with intervening telephone call-backs at approximately six-week intervals. There were 1210 adults in the 1976 survey and 931 cases in 1977. The initial interview contained questions on respondent's health beliefs, e.g. items on health values; and the final interview contained new questions on knowledge or perspective concerning cancer. At each call-back, respondents who reported having a health problem were queried in detail about their illness. If they did not report an illness, respondents were asked their opinion about certain health matters using a brief schedule that contained an eleven-item health locus of control scale. Sense of health control scores were thus obtained for 1054 respondents. In both 1976 and 1977 interviews, respondents were asked to indicate, which, if any, of nine-preventive health behaviors they engaged in over the preceding two months