© 2021 Ruijin Hospital, Shanghai JiaoTong University School of Medicine and John Wiley & Sons Australia, Ltd.Background: Coronavirus disease 2019 (COVID-19) has been reported to be associated with a more severe course in patients with type 2 diabetes mellitus (T2DM). However, severe adverse outcomes are not recorded in all patients. In this study, we assessed disease outcomes in patients with and without T2DM hospitalized for COVID-19. Methods: A nationwide retrospective cohort of patients with T2DM hospitalized with confirmed COVID-19 infection from 11 March to 30 May 2020 in the Turkish Ministry of Health database was investigated. Multivariate modeling was used to assess the independent predictors of demographic and clinical characteristics with mortality, length of hospital stay, and intensive care unit (ICU) admission and/or mechanical ventilation. Results: A total of 18 426 inpatients (median age [interquartile range, IQR]: 61  years; males: 43.3%) were investigated. Patients with T2DM (n = 9213) were compared with a group without diabetes (n = 9213) that were matched using the propensity scores for age and gender. Compared with the group without T2DM, 30-day mortality following hospitalization was higher in patients with T2DM (13.6% vs 8.7%; hazard ratio 1.75; 95% CI, 1.58-1.93; P <.001). The independent associates of mortality were older age, male gender, obesity, insulin treatment, low lymphocyte count, and pulmonary involvement on admission. Older age, low lymphocyte values, and pulmonary involvement at baseline were independently associated with longer hospital stay and/or ICU admission. Conclusions: The current study from the Turkish national health care database showed that patients with T2DM hospitalized for COVID-19 are at increased risk of mortality, longer hospital stay, and ICU admission.