This article presents findings from an analysis of occupational differentials in mortality among a cohort of males aged 55 years and older in the United States for the period 1966-1983. Using the National Longitudinal Survey of Mature Men, we construct event histories for 3,080 respondents who reach the exact age of 55. The dynamics that characterize socioeconomic differentials in mortality are analyzed by evaluating the differential effects of occupation over the career cycle. Maximum likelihood estimates of hazard-model parameters show that the mortality of current or last occupation differs substantially from that of longest occupation, controlling for education, income, health status, and other sociodemographic factors. In particular, the rate of mortality is reduced by the substantive complexity of the longest occupation while social skills and physical and environmental demands of the latest occupation lower mortality.