Introduction. On the 29th of October 2003, mitoxantrone was approved by the french health agency Afssaps (Agence française de sécurité sanitaire des produits de santé) for its use in the aggressive forms of multiple sclerosis (MS). It is the first immuno-suppressor having demonstrated particular efficacy in this progressive form of MS. Definition of aggressive MS. Agressive multiple sclerosis is defined as an MS that leads to the rapid accumumation of disabilities, whether these latter are the result of repeated relapses (at least 2 in the past 12 Months) or the continuous progression of a disability (increase in 2 points on the expanded disability status scale (EDSS) in the past 12 Months). The benefits of mitoxantrone. In cases of aggressive multiple sclerosis, mitoxantrone (20 mg IV), administered in Monthly cycles for 6 Months, clearly reduces the frequency of relapses, the appearance of new lesions on MRI and the progression of the disability. Precautions to be taken when using mitoxanthrone. The side effects however justify the fact that this drug is limited to the aggressive forms of MP. Cardiac toxicity limits the duration of the prescription and the maximum dose administered, requiring strict echocardiographical monitoring. Its unpredictable haematological toxicity can be devastating (risk of subsequent leukaemia). The benefit-risk ratio must be discussed with the patient and a Yearly echochardiography and three Monthly blood count must be continued during the 5 Years following withdrawal of mitoxantrone. The prescription of mitoxantrone is limited to the neurologists of departments specialized in neurology.