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.