Objective: This study aimed to evaluate the effect of categorized and normal vitamin D levels on hospital stay and mortality in adult patients with COVID-19. Methods: One hundred sixty-eight hospitalized patients due to coronavirus disease 2019 were retrospectively evaluated. The study data were collected from medical records (age, gender, comorbidity, vitamin D level, duration of hospital stay, mortality/ survival status). Serum 25(OH) vitamin D level ≥ 30 ng/mL is defined as normal, 20-29 ng/mL is an insufficiency level, and less than 20 ng/mL is defined as a deficiency level. Results: The mean vitamin D level of 168 patients was 18.72 ± 11.18 ng/mL, and 79.4% of patients with vitamin D deficiency had comorbidity. When vitamin D levels were categorized, there was no difference between the groups regarding hospital stay and survival (P > .05). However, when the mean vitamin D levels between the deceased and surviving patients were assessed, vitamin D levels were significantly higher in the survivors (P = .019). Vitamin D significantly affected survival compared to the univariate model (P = .044), while there was no significant effect on the multivariate model (P > .05). Even when the factors affecting the vitamin D level were adjusted, no significant results were found. Conclusion: Among hospitalized COVID-19 patients, vitamin D levels did not support an association between the duration of hospital stay and mortality.