The hypothesis that the quality of human relationships is a component in the development of cancer was investigated in a prospective study of former medical students. Findings from two psychological measures are presented: the Closeness to Parents Scale, which showed that students who subsequently developed cancer were more likely to describe a lack of closeness with their parents than their healthy classmates; and the Rorschach Interaction Scale, which demonstrated less satisfactory relationships among male cancer victims as contrasted with the rest of the cohort. The findings suggest that internal self-other representations, as measured by these two tests, are involved as regulators of biologic systems and manifestations of illness, such as cancer.