Background & Aims: It's been over 10 years that β-INF for the treatment of MS was presented to the world of medicine. As there are some doubts about the pathophysiology of MS, there may be some differences between our patients and other ones therefore,s such a study is essential for our patients.

Materials & Methods:�This is a descriptive-analytic and clinical trial study. According to clinical and para-clinical findings, the patients with the diagnosis of relapsing remitting MS were included in this study. Severity of disability (according to EDSS) and the number of attacks were estimated before and after the treatment with IFN β. Side effects of IFN β were evaluated too.

Results:�Among 42 patients, 73.8% were female and 26.2% were male. The mean age of onset was 29.21 years old. The mean relapsing rate before and after 1 year, 2 years, and 3 years of treatment were 2.43, 2.29, 3.28 and 0.57, 0.41 and 1.78 respectively the difference between these two was significant (P<0.05). The mean EDSS at the months of 0, 24 and 36 decreased significantly (P<0.05). The most common side effect of IFN-β in our study is flu like syndrome.

Conclusion:�Epidemiologic findings of this study such as M/F ratio and age of onset are similar to other studies. Statistical tests revealed the effects of IFN β on decreasing disabilities and relapse rate, but there are no differences of these effects between males and females.