Our study aimed to describe safety and neurological impact of alemtuzumab as last-line rescue therapy in aggressive multiple sclerosis (MS) patients, previously treated by Mitoxantrone (MITOX). Between June 2004 and October 2013, 13 patients received alemtuzumab at 20 mg/day and 3 at 12 mg/day for 5 days. EDSS, relapses, secondary progression were prospectively assessed 12 and 6 months before treatment, at baseline and every 3 months. Mean follow-up was 6.2 years [1-10]. Mean age at alemtuzumab start was 40 years [26-49] for 8 Secondary Progressive (SP) and 30 years [26-35] for 8 Relapsing-Remitting (RR) patients. MS duration was 13.7 (± 3) and 8.3 (± 4) years, respectively. During the 12 months before alemtuzumab, annual relapse rate was 0.75 and 3.14, respectively and the 16 patients accumulated 2-30 new gadolinium enhancing lesions. 4 patients (suboptimal responders) received alemtuzumab during MITOX and 12 patients 1-7.8 years after MITOX. Out of 8 SPMS, 2 were disease free up to last visit (4.7 and 8 years), 5 improved or stabilized but only transiently and 1 worsened. Out of 8 RRMS, 1 remained stable up to last visit (8.7 years) despite 1 relapse and active MRI at 18 months and 7 improved (1-4 point EDSS): 4 remained disease free up to last visit (12, 24, 38 months and 7 years), 2 were successfully retreated at 25 and 33 months and 1 worsened progressively 24 months after alemtuzumab. 2 patients developed Grave's disease and 1 hypothyroidism. Alemtuzumab controls aggressive RRMS despite previous use of MITOX.