Evaluation of: Adami S, Giannini S, Bianchi G et al.: Vitamin D status and response to treatment in post-menopausal osteoporosis. Osteoporos. Int. (2008) (Epub ahead of print). All recent osteoporosis guidelines recommend that patients taking treatments for osteoporosis (i.e., bisphosphonates) should be supplemented with vitamin D and calcium. However, the bone response (i.e., bone mineral density change and fractures incidence) to bisphosphonates therapy in relation to vitamin D intake in clinical practice is unknown. In a recent retrospective study, 1515 women with postmenopausal osteoporosis under antiresorptive treatment were classified as vitamin D deficient or vitamin D repleted, according to risk factors or the level of 25 hydroxy vitamin D above or below 50 nmol/l. The change in bone mineral density remained significantly higher in vitamin D-repleted compared with vitamin D-deficient women. Moreover, the adjusted odds ratio for incident fractures in vitamin D-deficient as compared with vitamin D-repleted women was 1.77 (95% CI: 1.20-2.59; p = 0.004).