question: PURPOSE. To assess and compare the serum 25OH-vitamin D levels in three cohorts of patients hospitalized due to acute illness, either related or not to a SARS-COV-2 infection. To investigate, in the patients group with SARS-COV-2 pneumonia, the possible relationship between the serum vit- amin D levels and both disease severity and mortality risk. METHODS. This is a retrospective case-control study. Serum 25OH-vitamin D levels were compared between patients with SARS-COV-2 pneumonia (COVID-19 group, 52 patients), and two control groups, including patients with pneumonia not related to SARS-CoV-2 (NO COVID1 group, 52 patients) and patients with a non-respiratory acute disease (NO COVID2 group, 52 pa- tients). RESULTS. No differences were found in the serum 25 OH-Vitamin D levels among the three groups. In the COVID-19 group, serum 25 OH-Vitamin D levels did not show significant associa- tion with mortality risk (p=0.12), Intensive Care Unit admission risk (p=0.36), inpatients duration (p=0.40) and remission time (p=0.33). Similar results were found for parameters estimating the dis- ease severity, such as basal PO2/FiO2 (p=0.77), worse PO2/FiO2 (p=0.41), basal D-dimer (p=0.46) and basal LDH (p=0.52). CONCLUSIONS. Our data do not show lower 25OH-vitamin D levels in the patients with SARS- COV-2 pneumonia compared to patients hospitalized for other acute illnesses. In the COVID-19 group the 25OH-vitamin D levels did not show significant correlation with a worse outcome.