In the contemporary United States, mortality is 60% higher for males than for females. Forty percent of the excess of male mortality is due to arteriosclerotic heart disease, which is more common among men in part because they smoke cigarettes more than women do, and apparently also because they more often develop the competitive, aggressive Coronary Prone Behavior Pattern. Men who do not develop this Behavior Pattern may have as low a risk of coronary heart disease as comparable women. Oophorectomy of young women may increase the risk of coronary heart disease, but administration of female hormones generally does not reduce 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 linked to behaviours which are encouraged or accepted more in males than in females: using guns, drinking alcohol, smoking, working at hazardous jobs, and seeming to be fearless. Thus, the behaviors expected of males in our society make a major contribution to their elevated mortality.