Objective: Osteoporosis is a secondary problem in multiple sclerosis (MS) patients. There have been only a few reports about the effect of interferon beta (IFNB) 1b on bone mineral density (BMD). We aimed to determine bone mass in patients using IFNB 1b. Methods: We enrolled 17 patients taking IFNB 1b (group I), 15 patients not taking IFNB (group II). We measured the BMD and T scores values and the patients were distinguished as normal, osteopenia and osteoporosis. Results: In the lumbar spine, there was no difference between groups I and II (p = 0.3). In the left femur, no significant difference was detected between groups I and II (p=1). There was an inverse correlation between the BMD at the both regions and the Expanded Disability Status Scale score (r= -0.39, p = 0.03; r = -0.52, p = 0.002, respectively). Conclusion: IFNB 1b may be used safely in MS patients, even in those undergoing pulse steroid therapies, because IFNB 1b has no effect on BMD. © 2010 IOS Press and the authors. All rights reserved.