Background: Multiple Sclerosis (MS) is a neurological disease that is clinically characterized by lesions in the central nervous system, relapsing fatigue, and pain. Despite evidence supporting the use of exercise for MS symptom management, low rates of participation in exercise are observed. Previous research suggests that exercise-related cognitive errors (ECEs) can cause individuals to struggle in making the decision to exercise and deter physical activity participation. Purpose: To examine the relationship between exercise- and disease-specific cognitions and their relationship to exercise and well-being. Methods: 150 adults (aged 18 and over) with MS who were ambulatory completed multiple questionnaires: demographic, self-report MVPA, walking ability, ECEs, behavioural responses to illness, MS symptom control self-efficacy, and psychological well-being. Results: Higher ECE scores were positively associated with maladaptive behavioural responses to illness and somatic cognitive errors (rs>.417, p-.224, p.05), but were negatively related to perceived walking ability (r=.371, p<.001). Increased levels of maladaptive behavioural responses to illness were negatively associated with self-regulatory efficacy to manage MS-related symptoms (r=.362, p<.001) and positively associated with somatic cognitive errors (r=.390, p<.01). Conclusion: This study was the first to demonstrate associations between ECEs and different illness- and mobility-related perceptions for individuals with MS. Future research should prospectively examine the role of ECEs in predicting mobility-related outcomes.