Multiple sclerosis (MS) is a debilitating neurological disease with few successful interventions available for alleviating symptoms. Physical activity (PA) may aid in alleviating symptoms; however, most individuals with MS are inactive. To promote PA within this population, it is important to identify key theoretical correlates of PA specific to them and then target these in PA interventions. The purpose of this study was to examine the role of self-efficacy and outcome expectations in explaining PA. Seventy-six participants completed a baseline questionnaire measuring these variables and a telephone follow-up 1 month later concerning PA behaviors. Regression analyses showed that self-efficacy (beta = .41) and outcome expectations (beta = .27) directly influenced PA, and that self-efficacy directly influenced outcome expectations (beta = .28). Therefore, to promote PA within this population, interventions should target both self-efficacy and outcome expectations. Individuals with MS need to better understand the benefits of PA and how it can alleviate or improve their symptoms.