Background: Walking impairment is one of the hallmark symptoms of persons with multiple sclerosis (PwMS) and affects activities of daily living and their quality of life. One aspect of quality of life is illness intrusiveness, which examines disruptions to meaningful activities due to chronic disease and/or its treatments. As such, PwMS with high levels of illness intrusiveness may have greater impairments in walking, even after considering their level of physical disability. However, there have been no studies examining the relationship between illness intrusiveness and walking impairment. Objectives: To 1) determine whether illness intrusiveness, as measured by the Illness Intrusiveness Ratings Scale (IIRS), contributes to PwMS walking and 2) evaluate its role as a mediator between physical disability and walking. Methods: A total of 153 PwMS were included in this analysis, which is a part of an ongoing, larger study. Walking ability was measured using two commonly utilized walking measures in MS: gait speed with the Timed 25-Foot Walk (T25FW) and perceived walking with the 12-item Multiple Sclerosis Walking Scale (MSWS-12). Demographics (age and gender), assistive device usage, and disability (Patient Determined Disease Steps; PDDS) were also collected at this one-time visit. Hierarchal regressions were performed to examine the relationship between walking and the IIRS, controlling for age, gender, PDDS, and use of assistance. If the relationship was significant, a mediation analysis was then conducted. Results: IIRS was a significant predictor of the MSWS-12, even after accounting for age, gender, PDDS, and use of assistance (? = 0.23, p <.001). There was a significant indirect effect of the PDDS on the MSWS-12 through the IIRS (b = 1.26, 95% CI [.65, 2.04]). However, the IIRS did not significantly contribute to performance on the T25FW (? = 0.08, p = .177). Conclusions: Illness intrusiveness is a significant contributor to perceived walking ability, but not on their actual gait speed, suggesting there may be psychological and behavioral components to perceived walking among PwMS.