Background The coronavirus disease (COVID-19) pandemic has brought significant challenges worldwide, with high mortality, increased use of hospital resources, and the collapse of healthcare systems. We aimed to describe the clinical outcomes of critically ill COVID-19 patients and assess the impact on the use of hospital resources and compare with critically ill medical patients without COVID-19. Methods and findings In this retrospective cohort study, we included patients diagnosed with COVID-19 admitted to a private ICU in Sao Paulo, Brazil from March to June 2020. We compared these patients with those admitted to the unit in the same period of the previous year. A total of 212 consecutive patients with a confirmed diagnosis of COVID-19 were compared with 185 medical patients from the previous year. Patients with COVID-19 were more frequently males (76% vs. 56%, p<0.001) and morbidly obese (7.5% vs. 2.2%, p = 0.027), and had lower SAPS 3 (49.65 (12.19) vs. 55.63 (11.94), p<0.001) and SOFA scores (3.78 (3.53) vs. 4.48 (3.11), p = 0.039). COVID-19 patients had a longer ICU stay (median of 7 vs. 3 days, p<0.001), longer duration of mechanical ventilation (median of 9 vs. 4 days, p = 0.003), and more frequent tracheostomies (10.8 vs. 1.1%, p<0.001). Survival rates until 28 days were not statistically different (91% vs. 85.4%, p = 0.111). After multivariable adjustment for age, gender, SAPS 3, and Charlson Comorbidity Index, COVID-19 remained not associated with survival at 28 days (HR 0.59, 95% CI 0.33–1.06, p = 0.076). Among patients who underwent invasive mechanical ventilation, the observed mortality at 28-days was 16.2% in COVID-19 patients compared to 34.6% in the previous year. Conclusions COVID-19 required more hospital resources, including invasive and non-invasive ventilation, had a longer duration of mechanical ventilation, and a more prolonged ICU and hospital length of stay. There was no difference in all-cause mortality at 28 and 60 days, suggesting that health systems preparedness be an important determinant of clinical outcomes.