This paper emphasizes the relationship of the patient's personality to the rate of growth of his neoplasm. The principal instrument used for this study was a battery of tests, of which the Minnesota Multiphasic Personality Inventory was found to be the most valuable. Patients with rapidly advancing cancer were found to be significantly different in psychological structure from those whose period of survival was far longer than the average expectancy. It is suggested that longstanding intense emotional stress may exert a profoundly stimulating effect on the rate of growth of an established cancer. The ability to reduce environmental