Introduction: Various biomarkers based on blood counts have been useful for the prognosis of patients critically ill with COVID-19. Objective: To describe the usefulness of the neutrophil-to-lymphocyte (NLR), monocyte-to-lymphocyte (MLR) and lymphocyte-to-platelet (LPR) ratios for the prognosis of mortality and ventilatory support requirement for COVID-19. Method: Retrospective cohort of clinical records of patients with COVID-19 who required hospital care. Results: One-hundred and -twenty-five cases were analyzed; mean age was 51 years, and 60 % were of the male gender; 21.6 % had type 2 diabetes mellitus, and 18.4 % had hypertension. Mean leukocyte count was 9.5 x 103/µL, with a neutrophil mean of 8.0 x 103/µL. Mean NLR was 12.01, while for MLR it was 0.442, and for LPR, 373.07. Regarding the area under the curve, the following values were recorded for mortality: 0.594 for NLR, 0.628 for MLR and 0.505 for LPR; as for mechanical ventilation, the values were 0.581 for NLR, 0.619 for MLR and 0.547 for LPR. In the univariate analysis, an NLR value > 13 (OR: 2.750, p = 0.001) and an MLR of > 0.5 (OR: 2.069, p = 0.047) were associated with mortality; LPR showed no impact on mortality or respiratory support. Conclusion: NLR and MLR are useful for predicting mortality in patients with COVID-19.