Bone mineral density (BMD) is affected in young adults with multiple sclerosis (MS), which leads to disabling disease. We aimed to show changes that were independent of immobilization by measuring BMD and laboratory markers of bone metabolism in mobile MS patients. We compared a total of 52 premenopausal female patients with relapsing-remitting multiple sclerosis (RRMS) to 41 women of similar age who had no risk factors for osteoporosis. The lumbar and femur BMD were measured using the dual energy X-ray absorptiometry (DXA) method. The urine concentration of serum 25-hydroxycholecalciferol (25-OH vit D(3)), and pyridinoline and deoxypyridinoline were also measured. The concentration of serum osteocalcin was measured to determine the speed of bone metabolism. The mean age of patients (+/- standard deviation [SD]) was 36.1 +/- 7.4. The average Expanded Disability Status Scale (EDSS) score was 2.2 +/- 1.8. The concentration of 25-OH vit D(3) and osteocalcin was lower, whereas the concentration of parathyroid hormone (PTH), alkaline phosphatase (ALP), pyridinoline and deoxypyridinoline was higher in the patient group. In the patient group, lumbar 2-4 BMD, T score and Z score and femur neck and trochantor BMD, T score and Z score were significantly lower than in the control group. There was a significant negative relationship between: the disease period and L 2-4 BMD, T score and Z scores: and the femoral neck BMD, T score and Z scores. There was a significant relationship between the total Functional Independence Measure score and the femoral neck, femoral trochanter BMD, T score, and Z score. There was a significant negative relationship between the average EDSS, L 2-4 and all the DXA measurements obtained from the femur. There was a significant relationship between the 25-OH vit D(3) concentration and L 2-4 T score and Z score from the DXA measurements obtained from the femur. There were no significant relationships between osteocalcin, pyridinoline, deoxypyridinoline levels and the BMD measurements. Therefore, the duration of the disease and decrease in functional capacity are the main factors that affect BMD in MS. Apart from the decrease in functional capacity, 25-OH vit D(3) deficiency and secondary PTH increase contribute to the BDM changes observed in MS. (C) 2010 Elsevier Ltd. All rights reserved.