Cyclophosphamide (CTX) is an alkylating agent related to nitrogen mustards whose anti-inflammatory and immunosuppressive effects have been utilised to treat selected cases of multiple sclerosis with a progressive and worsening course. To halt the progression of disease in patients refractory to disease modifying drugs CTX has been given, and several open-label studies have recently shown clinical benefits. In a previous study we demonstrated the effectiveness of a combination of IV monthly pulses of CTX and interferon beta (IFN-beta) in 10 patients with "rapidly transitional" form of multiple sclerosis characterised by severe and frequent attacks and rapid progression of disability. The present study reports the clinical and MRI follow-up 36 months after the discontinuation of CTX showing the maintenance of the results obtained in relapse rate (p<0.001), EDSS (p<0.001), T2 MRI total lesion load (p<0.001) and T2 lesions number (p<0.001) compared to the pre-treatment period. These encouraging findings and the absence of significant recorded side effects affirm that the association of CTX plus interferon-beta is amenable, safe and can be recommended in rapidly worsening MS patients.