Physicians have recognized for a long time that disease categories provide minimal information about the impact of illness on patient experiences. A diagnosis is important, because it can identify a course of treatment. However, there are considerable differences in how patients with similar diagnoses are affected. Multiple sclerosis, for example, may have essentially no impact on behavioral dysfunction or it could have devastating implications. The impact of the disease on the daily life of the patient may be more important than the diagnosis of the condition. Physicians need to learn to treat the patient, not the disease. There are only two health outcomes that are of importance. First, there is life expectancy. Second, there is function or quality of life. Biologic and physical events are mediators of these behavioral outcomes. We are concerned about cancer, high blood pressure, high cholesterol, and other problems because they may shorten a patient's life expectancy or make his or her life less desirable before death. There is a growing consensus that these behavioral outcomes are central in studies of health care and medicine. However, these outcomes, which can be obtained from standardized questionnaires, rarely are obtained in medical research and practice. A behavioral concept of health outcomes can suggest important new directions for research and practice.