Prior research has highlighted poor clinical outcomes in coronavirus disease 2019 (COVID-19)-infected patients with diabetes; however, susceptibility to COVID-19 infection in patients with diabetes has not been extensively studied. Participants aged ≥30 years who underwent COVID-19 testing from December 2019 to April 2020 were analyzed using the National Health Insurance Service data in South Korea. In a cohort comprising 29,433 1:1 propensity score-matched participants, COVID-19 positivity was significantly higher in participants with diabetes than in those without diabetes (512 [3.5%] vs. 395 [2.7%], P<0.001). Logistic regression analysis indicated that diabetes significantly increased the risk of COVID-19 test positivity (odds ratio, 1.307; 95% confidence interval, 1.144 to 1.493; P<0.001). Patients with diabetes exhibited heightened COVID-19 infection rates compared to individuals without diabetes, and diabetes increased the susceptibility to COVID-19, reinforcing the need for heightened preventive measures, particularly considering the poor clinical outcomes in this group.