The relations of agency (positive focus on self) and unmitigated agency (focus on self to the exclusion of others) to men's quality of life following prostate cancer was examined. Whereas agency was associated with indicators of a good quality of life, unmitigated agency was associated with indicators of a poor quality of life, particularly more intrusive thoughts about the illness, more depressive symptoms, and worse mental functioning over time. The primary psychological mechanism that explained these relations was reduced self-efficacy. Unmitigated agency was associated with feeling less capable of controlling the demands the illness imposed. Unmitigated agency also was associated with adverse changes in bowel and urine function; and changes in bowel and urine function explained the relation of unmitigated agency to poor quality of life.