Background: Few data are available on the rate and characteristics of thromboembolic complications in hospitalized patients with COVID-19. Methods: We studied consecutive symptomatic patients with laboratory-proven COVID-19 admitted to a university hospital in Milan, Italy (13.02.2020–10.04.2020). The primary outcome was any thromboembolic complication, including venous thromboembolism (VTE), ischemic stroke, and acute coronary syndrome (ACS)/ myocardial infarction (MI). Secondary outcome was overt disseminated intravascular coagulation (DIC). Results: We included 388 patients (median age 66 years, 68% men, 16% requiring intensive care [ICU]). Thromboprophylaxis was used in 100% of ICU patients and 75% of those on the general ward. Thromboembolic events occurred in 28 (7.7% of closed cases; 95%CI 5.4%–11.0%), corresponding to a cumulative rate of 21% (27.6% ICU, 6.6% general ward). Half of the thromboembolic events were diagnosed within 24 h of hospital admission. Forty-four patients underwent VTE imaging tests and VTE was con?rmed in 16 (36%). Computed tomography pulmonary angiography (CTPA) was performed in 30 patients, corresponding to 7.7% of total, and pulmonaryembolismwascon?rmedin10(33%ofCTPA).TherateofischemicstrokeandACS/MIwas2.5%and 1.1%, respectively. Overt DIC was present in 8 (2.2%) patients. Conclusions: The high number of arterial and, in particular, venous thromboembolic events diagnosed within 24 h of admission and the high rate of positive VTE imaging tests among the few COVID-19 patients tested suggestthatthereisanurgentneedtoimprovespeci?cVTEdiagnosticstrategiesandinvestigatethee?cacyand safety of thromboprophylaxis in ambulatory COVID-19 patients.