Introduction: In late 2019, the coronavirus disease (COVID-19) emerged in Wuhan, China. COVID-19 was characterized in March 2020 as a pandemic and has already caused a million deaths worldwide. Studies help clarify the clinical profile of this disease, repeatedly showing that the presence of morbidities such as type 2 diabetes mellitus (DM2) and its associated diseases (obesity, hypertension, and cardiovascular disease) are important risk factors for the severity and prognosis of the disease, in addition to advanced age. Therefore, this study aimed to analyze the association between COVID-19 and DM2 and clinical outcomes and mortality in patients admitted to a hospital in the metropolitan region of Porto Alegre, Rio Grande do Sul, Brazil. Methods: In this cohort study, we retrospectively reviewed 501 hospitalized patients with COVID-19, with or without diabetes, who were admitted between April 2020 and October 2021. Results: Diabetic patients were significantly older and presented more hypertension and cardiovascular disease. The most common symptoms at the onset of the disease in general were dyspnea, followed by dry cough, fever, myalgia, and fatigue. The DM2 was a risk factor independently associated with the outcomes of intensive care unit (ICU) care (32% increase), mechanical ventilation (30% increase), and hemodialysis (91% increase). Conclusions: The study concluded that patients with COVID-19 and DM2 had a significantly higher risk of ICU admission and a greater need for mechanical ventilation and hemodialysis, but DM2 was not a risk factor for increased mortality.