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Purpose. Individuals with diabetes carry an increased risk for adverse clinical outcome in case of SARS-CoV-2 infection. The purpose of this study was to evaluate whether this risk is, at least in part, modulated by an increase of thromboembolic complications. Methods. We prospectively followed 169 hospitalized patients with confirmed COVID-19 pneumonia admitted to the Internal Medicine Units of San Raffaele Hospital. We analysed inflammation and tissue damage biomarkers, hemostatic parameters, thrombotic events and clinical outcome according to the presence of hyperglycaemia or diagnosed diabetes. Results. Among 169 patients, 51 (30.2%) had diabetes. Diabetes and hyperglycemia were associated with increased inflammation and tissue damage circulating markers, higher D-dimer levels, increased prothrombin time and lower antithrombin III activity. Forty-eight venous and 10 arterial thrombotic events were identified in 49 (29%) patients. Diabetes (HR 2.71, p=0.001), fasting blood glucose (HR 4.32, p<0.001), glucose variability (HR 1.6, p < 0.009), presence of antiphospholipid antibodies (HR 4.18, p=0.033) and the positivity for virus spike protein antibodies (RBD IgG, HR 3.93, p=0.006; S1/S2 IgG, HR 3.36, p=0.027 and RBD IgA, HR 4.98, p=0.001) were all associated with an increased risk of thromboembolic complication. Thromboembolic complications significantly increased the risk for an adverse clinical outcome only in the presence of diabetes (HR 3.05, p=0.01) or hyperglycaemia (HR 3.07, p=0.015). Conclusions. Thromboembolism risk is higher among patients with diabetes and COVID-19 pneumonia and is associated to poor clinical outcome. In case of SARS-Cov-2 infection patients with diabetes could be considered for a more intensive prophylactic anticoagulation regimen.