The purpose of this study was to examine the demographic, medical, and social cognitive determinants of exercise intentions in a population-based sample of multiple myeloma cancer survivors. Using a cross-sectional survey, 70 multiple myeloma cancer survivors completed a questionnaire that assessed their medical and demographic characteristics, past exercise behavior, and social cognitive exercise beliefs using the theory of planned behavior. Seventy participants provided valuable data. Descriptive statistics indicated that participants had quite positive instrumental attitude, intentions, and subjective norms and moderate levels of perceived behavioral control and affective attitudes for exercise. Forced entry multiple regression showed that the theory of planned behavior explained 43% of the variance in exercise intentions. Instrumental attitude and perceived behavioral control were both independent predictors of exercise intentions. No demographic or medical variable moderated the association between the theory of planned behavior constructs and exercise intentions. The results of the present investigation support the growing body of evidence confirming the utility of the theory of planned behavior to understand the salient determinants of exercise in cancer survivors. Knowledge gained from this study provides important information to oncology practitioners who are responsible for delivering supportive care interventions, including exercise, to patients diagnosed with multiple myeloma.