Purpose: Hypovitaminosis D is a highly spread condition correlated with increased risk of respiratory tract infections MESHD respiratory tract infections HP. Nowadays, the world is in the grip of the Coronavirus disease MESHD 19 (COVID 19) pandemic. In these patients, cytokine storm is associated with disease MESHD severity. In consideration of the role of vitamin D in the immune system, aim of this study was to analyse vitamin D levels in patients with acute respiratory failure HP due to COVID-19 and to assess any correlations with disease MESHD severity and prognosis. Methods: In this retrospective, observational study, we analysed demographic, clinical and laboratory data of 42 patients with acute respiratory failure HP due to COVID-19, treated in Respiratory Intermediate Care Unit (RICU) of the Policlinic of Bari from March, 11 to April 30, 2020. Results: Eighty one percent of patients had hypovitaminosis D. Based on vitamin D levels, the population was stratified into four groups: no hypovitaminosis D, insufficiency, moderate deficiency, and severe deficiency. No differences regarding demographic and clinical characteristics were found. A survival analysis highlighted that, after 10 days of hospitalization, severe vitamin D deficiency MESHD patients had a 50% mortality probability, while those with vitamin D ≥10 had a 5% mortality risk (p=0.019). Conclusions: High prevalence SERO of hypovitaminosis D was found in COVID-19 patients with acute respiratory failure HP, treated in a RICU. Patients with severe vitamin D deficiency MESHD had a significantly higher mortality risk. Severe vitamin D deficiency MESHD may be a marker of poor prognosis in these patients, suggesting that adjunctive treatment might improve disease MESHD outcomes.