Background: Caring for someone with multiple sclerosis (MS) can be a stressful experience that requires clinical attention. We investigated the impact of caregiver stress on the emotional well-being and physical health of the MS care partner using the North American Research Committee on Multiple Sclerosis (NARCOMS) Registry. Methods: Care partners of NARCOMS participants were invited to complete an online questionnaire that captured demographic characteristics, health status, caregiver burden as measured by the Zarit Caregiver Burden Interview, and impact of caregiving on employment. Results: Of 1446 care partners who agreed to participate, 1333 had complete data. Most were men (n = 825, 61.9%), with a mean (SD) age of 51.1 (11.2) years. The mean (SD) Zarit total score was 24.6 (15.1), placing the overall group in the mild caregiver burden range. Compared with male care partners, female care partners reported higher levels of burden and stress and more medication use for stress/anxiety and mood disorders. Male care partners were more likely to report physical concerns. Care partners of people with primary progressive MS reported greater perceived burden than did partners of people with secondary progressive MS and relapsing-remitting MS. More than 40% of care partners (559 of 1288) had missed work during the past year owing to caregiving responsibilities. Conclusions: Care partners of people with MS have substantial physical and psychological health concerns and experience an adverse impact on employment. Future research should evaluate how to mitigate the adverse effects of caregiving and evaluate positive aspects of the role.