Purpose <p>This study aimed to elucidate how the admission of patients with coronavirus disease-2019 (COVID-19) to the intensive care unit (ICU) impacts the mortality rate and management of patients without COVID-19 in the ICU, focusing on the condition of patients during and after ICU admission, which has not been sufficiently evaluated.</p> Methods <p>This multicenter retrospective cohort study was conducted across 33 ICU facilities in Japan, using data from the Japanese Intensive Care Patient Database for fiscal years 2018–2020. Patients without COVID-19 were admitted to ICUs that also treated patients with COVID-19 during the study period. Of the 68,620 patients without COVID-19, 11,503 were admitted during the COVID-19 period. The primary outcome was in-hospital mortality. The secondary outcomes included ICU mortality, off-hour ICU discharge, ICU discharge with mechanical ventilation, and incidence of tracheotomy.</p> Results <p>Adjusted analyses revealed no significant difference in in-hospital mortality (adjusted odds ratio [aOR] = 0.90; p = 0.071) but lower ICU mortality (aOR = 0.75; p = 0.001) during the COVID-19 period. The COVID-19 period was associated with increased off-hour ICU discharges (aOR = 1.37; p &lt; 0.001), higher tracheotomy rates (aOR = 1.45; p = 0.018), and increased ICU discharges requiring mechanical ventilation (aOR = 1.21; p = 0.006). Moreover, ICU bed occupancy rates were lower in patients without COVID-19.</p> Conclusion <p>In-hospital mortality in patients without COVID-19 during the COVID-19 period was not significantly different from that during the non-COVID-19 period. While ICU mortality decreased, the tracheostomy rate, rate of patients requiring ventilators at the time of ICU discharge, and rate of transfer to other facilities increased.</p>