 Multiple sclerosis MS is an autoimmune disease characterized by progressive immune-mediated destruction of myelin and axons within the CNS. Despite the development, approval and clinical utilization of several medicines for patients with MS, most patients continue to accrue progressive disability. High-dose cyclophosphamide is chemotherapy treatment option for severe, refractory, immune-mediated illnesses such as MS. There is growing evidence that high dose cyclophosphamide is well tolerated and effective in MS. Our experience with 9 patients who underwent treatment at the Johns Hopkins Hospital yielded impressive results with a significant 40 reduction in baseline disability and an 81 reduction in MRI gadolinium enhancing lesions. Five out of 9 patients had recurrence of new brain MRI lesions during 24 months of follow-up, recurring in 4 patients during the first year of follow-up. Our findings suggest that high-dose cyclophosphamide holds promise in inducing remission and reducing disability in relapsing remitting MS however the recurrence of MS disease activity evidenced by worsening disability, clinical exacerbations or ongoing MRI evidence of new lesions suggests that high-dose cyclophosphamide given as a treatment on its own, is not sufficient to induce long-term remission. 