Infection with the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) poses an enormous challenge to health care systems throughout the world . Without causal treatment, identification of modifiable prognostic factors may help to improve outcomes . To explore possible associations of vitamin D (VitD) status with disease severity and survival, we studied 185 patients diagnosed with coronavirus disease 2019 (COVID-19) and treated at our center . VitD status at first presentation was assessed retrospectively using accredited laboratory methods . VitD deficiency was defined as serum total 25-hydroxyvitamin D level <12 ng/mL (< 30 nM). Primary endpoint was severe course of disease (i.e., need for invasive mechanical ventilation and/or death, IMV/D). Within a median observation period of 66 days (range 2-92), 23 patients required IMV . A total of 28 patients had IMV/D, including 16 deaths . Ninety-three (50 %) patients required hospitalization (inpatient subgroup). A total of 41 (22 %) patients were VitD deficient . When adjusted for age, gender, and comorbidities, VitD deficiency was associated with higher risk of IMV/D and death (HR 6.12 , 95% CI 2.79-13.42, <0.001 and HR 14.73 , 95% CI 4.16-52.19, <0.001, respectively). Similar correlations were observed in the inpatient subgroup . Our study demonstrates an association between VitD deficiency and severity/mortality of COVID-19, highlighting the need for interventional studies on VitD supplementation in SARS-CoV-2 infected individuals.