The purpose of this study was to evaluate the theory of planned behavior as a framework for understanding exercise intention and behavior in survivors of breast and prostate cancer. Participants were 83 survivors of breast and 46 survivors of prostate cancer who were diagnosed within the previous 4 years and had completed treatment. Each participant completed a mailed self-administered questionnaire that assessed exercise during the previous week, demographic and medical variables, and the theory of planned behavior. For survivors of breast cancer, regression analyses indicated that attitude, subjective norm, and perceived behavioral control explained 45% of the variance in exercise intention with attitude, subjective norm, and perceived behavioral control each uniquely contributing to intention. Furthermore, exercise intention explained 30% of the variance in exercise behavior; however, perceived behavioral control added no unique variance. For survivors of prostate cancer, attitudes, subjective norm, and perceived behavioral control explained 36% of the variance in exercise intention, but only perceived behavioral control made a significant unique contribution. Furthermore, intention explained 36% of the variance in exercise behavior; however, perceived behavioral control added no unique variance. Results suggest that nurses may use the theory of planned behavior as a model for understanding the determinants of exercise intentions and behavior in survivors of breast and prostate cancer.