This review focuses on the effects of psychosocial interventions on psychological and biological functioning of breast cancer patients. Once in their lifetime, one out of eleven women receive a diagnosis of breast cancer. A diagnosis of breast cancer is a severe stressful life event with profound consequences on all aspects of human life. Whether a woman will regain emotional balance and accept the idea of living with a potentially life threatening disease depends on her psychological resiliency. Provision of psychosocial interventions can improve these women's coping abilities and reduce emotional distress and feelings of isolation, and improve psychosexual functioning. Additionally, there exists some evidence that psychotherapy may prolong survival. Prolongation of survival may be related, in part, to an increase in certain aspects of immune function (e.g., natural killer cell activity). This is plausible because the function of the immune system seems to be related to mammary tumor growth. Therefore, future research should examine the degree to which the effects on mammary tumor growth relate to immune system changes.