Background: Fatigue, a major cause of disability in individuals with multiple sclerosis (MS), is associated with reduced quality of life. The aim of this study was to evaluate the reliability and reproducibility of the Persian version of Modified Fatigue Impact Scale (MFIS) in Iranian patients with MS.Methods: This study included 15 subjects with clinically definite MS, 15 hospitalized patients with MS, and 15 hospitalized patients with other chronic illnesses (as controls). They filled in the Persian version of the MFIS twice with a three-day interval. MFIS items were analyzed and the correlation coefficient was calculated.Results: There was a good correlation between the scores of the two measurements (correlation coe9cient: 0.984, P < 0.001) especially in physical and cognitive subgroups. The reproducibility of psychosocial subscale was lower than physical and cognitive subscales.Conclusion:According to our findings, the Persian version of the MFIS has a good reliability and reproducibility for assessment of fatigue in patients with MS.