© 2022 Via Medica. All rights reserved.Introduction: COVID-19 disease has a worse prognosis in patients with diabetes, but comparative data about the course of COVID-19 in patients with type 1 (T1DM) and type 2 diabetes (T2DM) are lacking. The purpose of this study was to find out the relative clinical severity and mortality of COVID-19 patients with T1DM and T2DM. Material and methods: A nationwide retrospective cohort of patients with confirmed (PCR positive) COVID-19 infection (n = 149,671) was investigated. After exclusion of individuals with unspecified diabetes status, the adverse outcomes between patients with T1DM (n = 163), T2DM (n = 33,478) and those without diabetes (n = 115,108) were compared by using the propensity score matching method. The outcomes were hospitalization, the composite of intensive care unit (ICU) admission and/or mechanical ventilation, and mortality. Results: The patients with T1DM had higher mortality than the age- and gender-matched patients with T2DM (n = 489) and those without diabetes (n = 489) (p < 0.001). After further adjustment for the HbA1c, and microvascular and macrovascular complications, the odds of mortality (OR: 3.35, 95% CI: 1.41-7.96, p = 0.006) and ICU admission and/or mechanical ventilation (OR: 2.95, 95% CI: 1.28-6.77, p = 0.011) were significantly higher in patients with T1DM compared to those with T2DM. Older age (OR: 1.06, 95% CI: 1.01-1.12, p = 0.028) and lymphopaenia (OR: 5.13, 95% CI: 1.04-25.5, p = 0.045) were independently associated with mortality in patients with T1DM. Conclusions: Patients with T1DM had worse prognosis of COVID-19 compared to T2DM patients or those without diabetes. These cases should be cared for diligently until more data become available about the causes of increased COVID-19 mortality in T1DM.