Background: Due to the unpredictable nature of COVID-19, there is a need to identify patients at high risk of severe course of the disease and a higher mortality rate. Objective: This study aims to find the correlation between frailty and mortality in adult, hospitalized patients with COVID-19. Methods: Clinical records of 201 patients who suffered from COVID-19 and were hospitalized between October 2020 and February 2021 were retrospectively analyzed. Demographic, clinical, and biochemical data were collected. Patients were assessed using Clinical Frailty Scale (CFS) and were divided into three groups: CFS 1–3 fit; CFS 4–6 vulnerable and with mild to moderate frailty; CSF 7–9, severe frailty. The association between frailty and in-hospital mortality was the primary outcome. Results: Severe frailty or terminal illness was observed in 26 patients (12.94%) from a cohort of 201 patients. Those patients were older (median age 80.73, p < 0.001) and had more comorbidities. Frailty was also associated with higher requirement for oxygen supplementation, greater risk of in-hospital complications and worse biochemical laboratory results. An increase in CFS score also correlated with higher mortality (OR = 1.727, p < 0.001). The Conclusions: Clinical Frailty Scale (CFS) can be used as a potentially useful tool in predicting mortality in patients with COVID-19.