Objective: The present study aims to evaluate vitamin D (Vit D) level in critically ill patients and to assess its level about morbidity and mortality. Materials and Methods: This study was conducted in an intensive care unit (ICU). Vit D level was measured on admission, third and seventh day. Results: Of the 62 patients, the median Vit D level at baseline and on the third and seventh days was 12.8 mcg/L, 8.35 mcg/L, and 9.30 mcg/L, respectively. Vitamin D level was low (<30 mcg/L) in 92% of patients at baseline and 97% on the third day. 23% of the studied patients developed a new site infection. No statistically difference in the Vit D level at baseline, or on the third or seventh day based on the presence of infection (p=0.556, p=0.404, p=0.439, respectively). The most commonly seen infections were ventilator-associated pneumonia (VAP) and catheter-related bloodstream infection (CRBSI). The growth of Acinetobacter baumannii was the most frequent. Vit D level (p>0.05) might not have a causal role in mortality (ICU, 30-day, and 6-month), and no correlation was found between them. Conclusion: The level of Vit D was low. Our study did not show any relationship between mortality rates and Vit D level, but VAP and CRBSI were observed. Keywords: Acinetobacter baumannii, critical illness, intensive care unit, mortality, new site infection, vitamin D