Socioeconomic status is positively related to health. Differences by socioeconomic status in health are closely related to differences in intelligence. This dissertation presents an investigation of the effects of health on intelligence and an investigation of the relationship between intelligence and the behaviors that affect health. One of the most important themes to emerge from this research is that the relationship between socioeconomic status and health may be driven in part by differences in success at self-control. The behaviors people choose affect their health. Some behaviors, such as the use of addictive substances, are influenced by failures of self-control. Psychologists have repeatedly demonstrated in the laboratory that more intelligent people tend to be better at self-control. Multiple regression analysis of data from a national survey is used to provide evidence that the relationship between intelligence and health is driven in part by differences in success at self-control. Implications for policies to improve the health of those with low socioeconomic status are discussed.