Breast cancer is a public health problem in the United States, with an estimated 182,000 new cases occurring in women in 1994. For most women, a diagnosis of breast cancer marks the beginning of a lifelong struggle. The disease and treatments become physical-psychological stressors whose effects linger long after the individual is tumor-free. This chapter examines the inherent psychosocial stressors that accompany a cancer diagnosis and the psychophysiologic effects that may occur as a result of these stressors. The physiologic and psychological stressors have been shown to profoundly influence neuroimmunoendocrine functioning. Some recent evidence indicates that psychosocial interventions designed to alleviate the cancer patients distress may affect disease progression and survival time, as well as improve quality of life. Three domains that may play a role in moderating health outcome are personality and coping characteristics, level of emotional expression, and social support.