The aim of this study was to assess the prognostic value of vitamin D, vitamin D binding protein (VDBP) and vitamin D-related peptides in septic shock patients in relation to hospital mortality. This is a single-center, prospective, observational study that included all consecutive patients meeting criteria for septic shock who were admitted to the ICU. VDBP, 25-hydroxy vitamin D, 1,25-dihydroxy vitamin D, cathelicidin and beta-defensin levels were determined in blood samples obtained on admission to the ICU. Seventy-five patients were studied. The best area under the curve (AUC) for prediction of in-hospital mortality was for VDBP (0.78), with a negative predictive value of 85.45% for the optimal cut-off point. VDBP was also the only variable that had a statistically significant association with a higher risk of in-hospital mortality, regardless of other assessed variables and pre-determined confounders: adjusted odds ratio of 5.20 (95% confidence interval: 1.21-22.36). When restricted to patients with vitamin D insufficiency (n=54), the AUC was 0.77, and the adjusted OR 12.22 (95% CI: 1.46-102.14; p=0.021) for in-hospital mortality. VDBP levels showed a statistically significant association with in-hospital mortality, supporting the clinical utility of VDBP as a good prognostic marker in septic shock patients. Vitamin D and vitamin D-related peptides are not associated with in-hospital mortality. These results should be confirmed in a multicentre study with a larger sample size. Copyright © 2018. Publicado por Elsevier España, S.L.U.