Background/aim: A prospective observational study was conducted to determine the relationship between vitamin D de ciency and nosocomial infections among intensive care unit (ICU) patients. Materials and methods: Demographic data, season of admission, vitamin D levels at admission, premorbid lifestyle scores, comorbid conditions, and admission diagnosis were recorded in 306 ICU patients. Infections that developed at least 48 h a er admission to the ICU were the primary outcome, and ICU, hospital, and 1-year mortality were the secondary outcomes. Infections were evaluated for 28 days, and for the entire duration of ICU stay independently. Multiple logistic regression analysis was performed to control for confounding factors that were statistically signi cant in univariate analysis. Results: All infection and mortality rates were signi cantly higher in low 25 (OH) D groups in univariate analysis. A er adjusting for confounding factors, infection rates remained higher in the de cient group. However, ICU and hospital mortality did not show any statistically signi cant di erence between de cient and nonde cient groups. Only the 1-year mortality rate was signi cantly higher among patients with 25 (OH) D levels less than 20 ng/mL. Conclusion: Low vitamin D levels are signi cantly associated with ICU-related infections but not with ICU or hospital mortality. However, further studies are needed to identify the role of vitamin D de ciency in predicting ICU outcomes.