Treatment side effects after radical prostatectomy include urinary, sexual, and bowel dysfunction. These functional declines, coupled with the bother associated with these dysfunctions, lead to a complicated pattern of change in quality-of-life and decreased self-efficacy.In this study, 72 men who underwent radical prostatectomy 6-weeks prior were randomly assigned to usual health care control group or peer-to-peer support (dyadic support) group. The dyadic meetings were held once a week for 8 weeks. Measured pre- and post-test was general health-related quality-of-life (SF-36), prostate cancer-specific quality-of-life (UCLA Prostate Cancer Index), and self-efficacy (Stanford Inventory of Cancer Patient Adjustment).By 8 weeks, self-efficacy significantly improved for men in the experimental group, but not for men in the control group. A series of logistic regression analyses showed that the dyadic intervention significantly accounted for changes in physical role functioning, bowel function, mental health, and social function. Age, education, and self-efficacy had significant interaction effects and increased the effects of the dyadic intervention on several outcomes.The intervention had a significant impact on how men react socially and emotionally to the side effects of radical prostatectomy.