Introduction: COVID-19 hospitalizations and deaths have raised the need of identifying prognostic factors for medical decision-making. Methods: Observational, retrospective study analyzing 191 COVID-19 patients' serum inflammatory biomarkers. Results: The median age was 48.7 ± 12.7 years, 75.9% being men. Overweight/obesity was the most common comorbidity in 83.8% of patients. 44.5% had moderate disease followed by 43.5% with severe disease. The mean percentage of pulmonary damage was 53.4% ± 28.7. Serum leukocyte-to-lymphocyte ratio >7.7, neutrophil-to-lymphocyte ratio >10, platelet-to-lymphocyte ratio ≥250 and nutritional index <362 all were independent mortality predictors for COVID-19. Conclusions: A leukocyte-to-lymphocyte ratio >7.7 as well as a nutritional index <362 at hospitalization were independently associated with an increased mortality.