Background: The efficacy of mitoxantrone induction therapy in rapidly worsening multiple sclerosis (MS) is well established. Plasma exchange is also applied as an adjuvant in exacerbations of relapsing MS. The aim of this study was to compare the efficacy of combination therapy with mitoxantrone and plasma exchange versus mitoxantrone alone in patients with aggressive MS. Materials and Methods: Forty patients with aggressive relapsing remitting MS were randomly put into two groups. The first group underwent monthly plasma exchange for three successive months, followed by 12 mg/m2 mitoxantrone at the end of each course and two more doses of 6 mg/m2 mitoxantrone in 3-month intervals. The second group received the same doses of mitoxantrone only without plasma exchange. At the end of 8 months treatment course, clinical reassessment and neuroimaging was performed and treatment was continued with interferon-β. Results: At the end of induction therapy, Expanded Disability Status Scale score was significantly improved in both groups (P < 0.001). Number of demyelinating and gadolinium-enhancing plaques in brain magnetic resonance imaging (MRI) was prominently reduced in group 2(P ≤ 0.05), but the changes were not statistically significant in group 1, except for juxtacortical plaques. Conclusion: Administration of mitoxantrone as an induction therapy in patients of aggressive relapsing remitting MS results in significant improvement of their clinical state and MRI activity. However, combination of plasma exchange with mitoxantrone gives no more benefits than mitoxantrone alone and sometimes worsens the situation possibly by reduction of mitoxantrone efficacy as a result of plasma exchange.