Background: Multiple sclerosis (MS) is a demyelinating disease which can cause many disabilities for the patient. Recent data suggests that MS patients have higher risk for osteoporosis. This study was performed to investigate if the osteoporosis prevalence is higher in MS patients and to determine the possible factors affecting bone mineral density (BMD).Methods:51 definite relapsing-remitting MS patients according to McDonald's criteria (45 females, 6 males aged between 20 and 50 years) participated in this study. The control group included 407 females aged from 20 to 49 years; they were healthy and had no history of the diseases affecting bone metabolism. Femoral and lumbar BMD were measured by Dual Energy X-ray Absorptiometry (DXA). The disability of MS patients was evaluated by Expanded Disability Status Scale (EDSS).Results:The patient's quality of life was evaluated by the validated Persian version of multiple sclerosis impact scale (MSIS-29).Patients' mean age was 36 ± 3.3 years and their mean disease duration was 8.7 ± 1.7 years. The mean EDSS score and the mean body mass index (BMI) of the patients were 3 ± 0.9 and 23.5 ± 2.3 kg/m(2), respectively. 29% of the patients had never been treated by ß-interferon and 6% of them had not received glucocorticoids (GCs) pulses since their MS had been diagnosed. 26% of the patients had a history of fracture.18% of our patients were osteoporotic and 43% of them were osteopenic. Femoral BMD was significantly lower among MS patients than age matched controls (P < 0.001), but lumbar BMD showed no difference. There was no correlation between administration of GCs pulses, interferon and BMD; however, we found a significant correlation between EDSS score, quality of life (QoL), disease duration and BMD of both site.Conclusion:As a result of this study, bone loss inevitably occurs in MS patients.The major factor of BMD loss is immobility. Osteoporosis should be managed as part of MS patients' treatment protocols.