In the contemporary U.S., mortality is 60% higher for males than for females. Forty percent of this sex differential in mortality is due to a twofold elevation of arteriosclerotic heart disease among men. Major causes of men's higher rates of arteriosclerotic heart disease include greater cigarette smoking among men and probably a greater prevalence of the competitive, aggressive Coronary Prone Behavior Pattern among men. Men who do not develop the Coronary Prone Behavior Pattern may have as low a risk of coronary heart disease as comparable women. Oopherectomy of young women may increase the risk of coronary heart disease, but administration of female hormones generally does not reduce the risk. One third of the sex differential in mortality is due to men's higher rates of suicide, fatal motor vehicle and other accidents, cirrhosis of the liver, respiratory cancers and emphysema. Each of these causes of death is related to behaviors which are encouraged or accepted more in males: using guns, drinking alcohol, smoking, working at hazardous jobs and being adventurous and acting unafraid. Thus the behaviors expected of males in our society make a major contribution to their elevated mortality. This analysis leads to suggestions for the reduction of male mortality, for example, by changing the social conditions which foster in men the behaviors which elevate their mortality.