The epidemiological and clinical characteristics, treatments, and outcomes of patients with coronavirus disease 2019 (COVID-19) who are admitted to the intensive care unit (ICU) have not been adequately evaluated in Japan. We analyzed the registry data of 205 patients with COVID-19 admitted to the ICU between February and November 2020, in Osaka Prefecture, Japan. A Cox proportional hazards model was used to assess the association between epidemiological factors and mortality among ICU patients. Of the 205 ICU patients, 161 (78.5%) were men and 149 (72.7%) were older than 60 years. A total of 117 patients (57.1%) had comorbidities. The most common symptoms at diagnosis were mild (n = 131, 63.9%). A total of 187 patients (91.2%) received mechanical ventilation, and 32 patients (15.6%) required extracorporeal membrane oxygenation. Patients were followed up for a median of 25 days after ICU admission. A total of 147 patients (71.7%) were alive at discharge, and 58 patients (28.3%) died. The hazard ratio for mortality among patients aged >80 years was 6.02 (95% confidence interval: 2.10−17.25) in the multivariable model, which was higher than that among those aged ≤59 years. These results are useful for recognizing the clinical course of this infection in ICU patients.