Background: People with multiple sclerosis have high risk of osteoporosis and fractures. A poor vitamin D status is a risk factor for MS, and vitamin D supplementation has been recommended both to prevent MS progression and to maintain bone health. Methods: We assessed the effect of 20,000 IU vitamin D-3 weekly compared to placebo on biochemical markers of bone metabolism in 68 persons with relapsing remitting multiple sclerosis. Results: Serum levels of 25-hydroxyvitamin D more than doubled in the vitamin D group, and parathyroid hormone decreased in the vitamin D group compared to the placebo group at week 48 and week 96. There was however no effect on bone formation as measured by procollagen type I N propeptide (PINP), or on bone resorption as measured by C-terminal cross-linking telopeptide of type I collagen (CTX1). Neither PINP nor CTX1 predicted bone loss from baseline to week 96. Conclusions: These findings corroborate the previously reported lack of effect of weekly high dose vitamin D supplementation on bone mass density in the same patients, and suggest that such vitamin D supplementation does not prevent bone loss in persons with MS who are not vitamin D deficient.