The relationships between psychological variables and the presence of cancer, its prediction, and the prediction of cancer mortality and course of disease have been studied extensively. From a limited list of about 50 such variables, the following have been the focus of the most intensive research and are discussed in this report: human and animal stress; bereavement; depressed mood; psychosis, especially schizophrenia; suppression of emotions, especially anger; helplessness and hopelessness; social support; and psychotherapeutic intervention. For all of these variables, studies have shown both positive relationships and absence of relationships. The evidence against any such relationship is strongest for human stress, depressed mood, psychosis, and bereavement. Studies of animal stress show that it stimulates the development of cancers of viral origin and exacerbates their growth, while inhibiting the development and progression of chemically induced cancers. For the other factors, the literature remains contradictory.