No effective treatment is presently available for progressive multiple sclerosis (MS). Cyclophosphamide (CFX), a cytotoxic immunosuppressive drug widely used in systemic dysimmune diseases, has been proposed for the treatment of multiple sclerosis with different schedules and controversial results. To evaluate the safety and clinical efficacy of CFX, we compared three different treatment schedules in patients with progressive MS: induction followed by bimonthly boosters for one year (17 patients); bimonthly boosters for one year without previous induction (15 patients); and monthly boosters for one year (21 patients). Survival analysis showed that the percentage of stable patients was significantly higher in the first and third treatment schedule groups. Myelotoxicity occurred in patients treated with induction and boosters (Group A). A high incidence of broncopneumonia was observed in patients undergoing the second treatment schedule (Group B). No major effects were observed in patients treated with monthly boosters (Group C). Response to treatment was limited to secondary progressive form. This study suggests that monthly treatment with CFX might be safely administered in progressive MS patients; its clinical efficacy must be confirmed by an appropriately designed clinical trial.