While the barriers and facilitators of physical activity adherence are well-defined, there is a limited number of studies focusing specifically on exercise adherence, which is crucial to identify in patients with multiple sclerosis (MS) due to its known disease-modifying effect. To investigate the factors affecting adherence to physical exercise in MS patients. Literature search was conducted in PubMed, Cochrane, Web of Science, and Scopus electronic databases up to the current date. Methodological quality was assessed using the Newcastle-Ottawa Scale (NOS) for quantitative studies and the McMaster Critical Appraisal Tool for qualitative studies, with evidence synthesis conducted using the Modified Bakker Scale. The systematic review incorporated thirteen studies, consisting of seven qualitative and six quantitative ones. These studies' methodological quality was high; 12 were high, and the other was medium (unclear). In all reviewed studies, the primary patient-related and environmental barriers with high levels of evidence regarding exercise adherence included fatigue (38%), false beliefs (18%), cost (18%), and lack of time (15%). Barriers identified in very few studies included cognitive problems (3%), bladder-bowel problems (3%), and family support and advice (3%), indicating a necessity for further research to reveal their impact on exercise adherence. The scarcity of studies on exercise barriers in MS is partly due to the absence of reliable assessment methods for evaluating exercise adherence, along with the prevalent emphasis on physical activity. Future research should prioritize the development of adherence scales tailored to physical exercise and shifting focus towards less explored barriers.