Background: In this study, it was aimed to evaluate the factors affecting the prognosis and mortality of patients hospitalized for coronavirus disease 2019 (COVID-19).Methods: Patients hospitalized with COVID-19 infection between March and November 2020 were examined retrospectively. The Systemic Immune-Inflammation Index (SII), platelet lymphocyte ratio (PLR), and neutrophil-lymphocyte ratio (NLR) values were evaluated for their effect on prognosis.Results: Of the 1013 patients included in the study, 204 (20.1%) had a severe infection. In the multivariate analysis, it was determined that the prognosis was significantly worse in patients who were >65 years of age, had a Charlson Comorbidity Index (CCI) score of >2, and had a high NLR rate. The C-reactive protein (CRP), PLR, SII values were detected as insignificant variables. Mortality was found to be statistically significant in patients with a CCI score of 2 or more and in patients with high CRP, NLR, PLR, and SII values at the time of admission (p