Cyclophosphamide (cy) is an alkylating agent used to treat malignancies and immune-mediated inflammatory nonmalignant processes. It has been used as a treatment in cases of worsening multiple sclerosis (MS). Cy is currently used for patients whose disease is not controlled by beta-interferon or glatiramer acetate as well as those with rapidly worsening MS. The most commonly used regimens involve outpatient IV pulse therapy given with or without corticosteroids every 4 to 8 weeks. Side effects include nausea, headache, alopecia, pain, male and women infertility, bladder toxicity, and risk of malignancy. Previous studies suggest that cy is effective in patients in the earlier stages of disease, where inflammation predominates over degenerative processes. Given that early inflammatory events appear to correlate with later disability, a major question is whether strong anti-inflammatory drugs, such as cy, will have an impact on later degenerative changes if given early in the disease to halt inflammation.