Objective: Risk factors affecting mortality in the coronavirus disease-2019 (COVID-19) pandemic, which emerged in Wuhan, China and affected the whole world, are yet to be clearly determined. Assessment of Charlson comorbidity index (CCI) and pneumonia severity index (PSI) can assist clinicians in identifying patients at high risk of mortality. This study aimed to determine the relation between CCI, indicating comorbidity burden in COVID-19 infection, and PSI, indicating disease severity, and their relationship with mortality. Materials and Methods: This was a retrospective cohort study conducted by accessing demographic, clinical and laboratory data from the electronic medical records of 214 patients diagnosed with COVID-19. The patients were followed up in the intensive care unit of University of Health Sciences Turkey, İstanbul Bakırköy Dr. Sadi Konuk Training and Research Hospital between March 10, 2020 and June 1, 2020. Results: Patients were divided into two groups i.e., survivors (n=109; 50.9%) and those with mortality (n=105; 49.1%). A one point increase in CCI was determined to increase the mortality probability by 32% [odds ratio (OR): 1,324, 95% confidence interval (CI): 1,178-1,488]. On the other hand, a one-point increase in PSI increased the mortality possibility by 2% (OR: 1,020, 95% CI: 1,012-1,0,27). In the correlation analysis performed to determine the relationship between CCI and PSI, a bidirectional and strong correlation was found between CCI and PSI (p<0.001, r=0.667). Conclusion: As a model for summarizing the sum of age and comorbidities, CCI can help identify patients at high mortality risk in the COVID-19 pandemic. Moreover, PSI may be useful in patients with low CCI scores for predicting mortality in COVID-19 patients; however, has not been found reliable in patients with high CCI scores.