Research has found suggestive links between emotional distress and immune and neuroendocrine measures in cancer patients. Furthermore, several studies have reported that participation in psychological support groups is associated with better health outcomes for cancer patients. However, controversy exists surrounding these findings, and the mechanisms behind such effects are unclear. This article integrates current evidence from several lines of research concerning the relations among coping, psychological adjustment, cortisol and immune function, and disease progression in breast cancer patients. A biopsychosocial model is evaluated in which coping and psychological adjustment are associated with alterations in cortisol levels, immune function, and potential long-term medical outcomes in breast cancer patients. Although strong evidence suggests that coping and psychosocial intervention can improve psychological outcomes for breast cancer patients, potential effects on physiological outcomes remain speculative.