Tehran University of Medical Sciences Current Journal of Neurology 2717-011X 10 1-2 2011 06 15 32 4 Seyed Massood Nabavi MS Research Unit, Neurology Department, Shahed University, Tehran, Iran. Ali Hamzehloo MS Research Unit, Neurology Department, Shahed University, Tehran, Iran Jalaledin Shams Hematology-oncology Unit, Internal Medicine Department, Shahed University, Tehran, Iran Damineh Morsali Medical School at Houston, Texas 2015 10 17 Background: Interferon beta-la and -1b have been increasingly used for the treatment of multiple sclerosis (MS). The most frequent systemic adverse effects are flu-like symptoms. Laboratory abnormalities include asymptomatic leukopenia and elevated hepatic transaminases. Myelodysplastic Syndrome (MDS) refers to a spectrum of hematological disorders which can occur in different situations. Several hematological abnormalities have been reported following interferon therapy. Methods: We report two cases of secondary MDS after long term interferon therapy by using the laboratory data and bone marrow results. Conclusion: Both of our cases were reversible; although treatment with IFNβ-1a and-1b is safe and well tolerated in the majority of population, we should be careful about this premalignant hematological disorder. https://ijnl.tums.ac.ir/index.php/ijnl/article/view/849 https://ijnl.tums.ac.ir/index.php/ijnl/article/download/849/107