Background: Increasing data suggests a connection between vitamin D (vitD) and COVID-19. VitD may impact COVID-19 by affecting innate cellular immunity and exacerbating cytokine storms linked to severe respiratory syndrome from the virus. Objective: To assess the prevalence of vitD deficiency in COVID-19 patients hospitalized at Hospital Ernesto Dornelles and examine its links to in-hospital mortality, the need for Intensive Care Unit (ICU), patient demographics, and hospital stay duration. Methods: A cross-sectional study was performed, in which 3518 hospitalized patients with a confirmed diagnosis of COVID-19 were evaluated to obtain the prevalence of vitD deficiency, from March 2020 to August 2022. Data collection was performed using electronic medical records, excluding patients without serum levels of vitD measured during hospitalization, and including those with the exam in their medical records, which were later placed for statistical analysis. Results: 486 patients had their serum level of vitD measured, with a mean age of 68.3 years, 57.2% female, and 42.8% male. The prevalence of vitD deficiency was 60.1% (292 patients). There was no difference between the groups with and without vitD deficiency when comparing age, gender, and comorbidities. The median length of hospital stay, the need for ICU admission, and the outcome of death were significantly higher in the group with vitD deficiency (p<0.001; p=0.005; p=0.03). After adjusting for confounding factors, only the risk of ICU admission remained 1.38x higher in the group with vitD deficiency than in the group without (p=0.015), as well as age and CRF were factors with a higher risk for ICU admission. Conclusions: The prevalence of vitD deficiency in patients with COVID-19 was 60%, being associated with a higher risk of ICU admission, possibly presenting or not an association with higher mortality rates and length of stay. Therefore, further studies are needed to establish a cause-and-effect association.