The aim of this study was to determine the possible factors affecting bone mineral density (BMD) in multiple sclerosis (MS). In this cross-sectional study, 65 clinically definite MS patients and 72 comparable controls were prospectively evaluated. To assess bone mineral metabolism in MS, the BMD of the lumbar spine and hip (femoral neck, trochanter and total) was measured by dual-energy X-ray absorptiometry, and serum vitamin D and parathyroid hormone levels and biochemical markers of bone turnover were also evaluated. MS patients had significantly lower BMD values than the control group at all measurement sites. There was a significant correlation between the disease duration and BMD values at the trochanter in women with MS. A correlation between femoral BMD values and functional status in women was also detected. There was no relationship between bone biochemical markers and BMD, except a negative correlation between bone alkaline phosphatase and trochanter BMD. Both disability and disease duration have an influence on BMD of the MS patients, whereas no significant correlation between glucocorticoid use and BMD was observed.