Tehran University of Medical Sciences Current Journal of Neurology 2717-011X 14 2 2015 06 15 81 85 Ghazaleh Eskandari Brain and Spinal Injury Research Center, Neuroscience Institute, Tehran University of Medical Sciences, Tehran, Iran. Mahsa Ghajarzadeh Brain and Spinal Injury Research Center, Neuroscience Institute, Tehran University of Medical Sciences, Tehran, Iran. Mir Saeed Yekaninejad Department of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran. Mohammad Ali Sahraian MS Research Center, Neuroscience Institute, Tehran University of Medical Sciences, Tehran, Iran. Razieh Gorji Iranian Center of Neurological Research, Tehran University of Medical Sciences, Tehran, Iran. Faezeh Rajaei Iranian Center of Neurological Research, Tehran University of Medical Sciences, Tehran, Iran. Abbas Norouzi-Javidan Brain and Spinal Injury Research Center, Neuroscience Institute, Tehran University of Medical Sciences, Tehran, Iran. Alireza Faridar Department of Neurology, Houston Methodist Hospital, Weill Cornell Medical College, Houston, TX. Amirreza Azimi Brain and Spinal Injury Research Center, Neuroscience Institute, Tehran University of Medical Sciences, Tehran, Iran. 2015 10 14 Background: Multiple sclerosis (MS) is an autoimmune,  neuro- inflammatory disease  of  central nervous system affecting physical, emotional, and cognitive aspects of patients. Association of vitamin D deficiency and MS has been shown in previous studies. The aim of this study was to evaluate serum vitamin D level in MS cases and their sex-matched healthy siblings (who are genetically near similar) and non-relative sex-matched healthy controls. Methods: A total of 135 subjects enrolled in this case- control study. Group one (n = 45) consisted of patients with established MS. Group two (n = 45) included sex- matched healthy siblings of the group one and group three participants (n = 45) were non-relative sex- matched  healthy  controls.  Demographic  data  (age, sex), level of education, daily sun exposure duration, and month of birth gathered for all. Serum sample of all participants was collected for 25-hydroxy vitamin D measurement. Results: There was no significant difference between vitamin D level, sun exposure duration, education level, and season of birth in three evaluated groups. Mean vitamin D level was 8.2 ± 10.1 (nmol/l) in women and 13.3 ± 7 (nmol/l) in men (P = 0.001). There was a significant positive correlation between daily sun exposure duration and vitamin D level in whole participants (r = 0.28, P < 0.001) as well as in MS patients (r = 0.32, P = 0.030). Mean vitamin D level was significantly lower  in  participants  who  have  born  in spring and summer. Conclusion:  Vitamin  D  deficiency  is  high  among Iranian population as well as MS patients. https://ijnl.tums.ac.ir/index.php/ijnl/article/view/566 https://ijnl.tums.ac.ir/index.php/ijnl/article/download/566/236