more than 1) occurred in 533 (16.0%) patients; 207 (6.2%) were venous (3.2% PE and 3.9% DVT) and 365 (11.1%) were arterial (1.6% ischemic stroke, 8.9% MI, and 1.0% systemic thromboembolism; Table 1). Following multivariable adjustment, age, sex, Hispanic ethnicity, coronary artery disease, prior MI, and higher D-dimer levels at hospital presentation were associated with a thrombotic event (Table 2). All-cause mortality was 24.5% and was higher in those with thrombotic events (43.2% vs 21.0%; P < .001) (Table 1). After multivariable adjustment, a thrombotic event was independently associated with mortality (adjusted hazard ratio, 1.82; 95% CI, 1.54-2.15; P < .001). Both venous (adjusted hazard ratio, 1.37; 95% CI, 1.02-1.86; P = .04) and arterial (adjusted hazard ratio, 1.99; 95% CI, 1.65-2.40; P < .001) thrombosis were associated with mortality (P = .25 for interaction). Among 829 ICU patients, 29.4% had a thrombotic event (13.6% venous and 18.6% arterial). Among 2505 non-ICU patients, 11.5% had a thrombotic event (3.6% venous and 8.4% arterial). Discussion | In patients with COVID-19 hospitalized in a large New York City health system, a thrombotic event occurred in 16.0%. D-dimer level at presentation was independently associated with thrombotic events, consistent with an early coagulopathy. Prior studies varied regarding the precise incidence of thrombosis; however, all suggested a heightened risk in patients with COVID-19. 3,4 This analysis found variation by clinical setting and type of thrombosis event. While thrombosis is observed in other acute infections 5 (eg, 5.9% prevalence during the 2009 influenza pandemic), 6 the thrombotic risk appears higher in COVID-19. Thrombosis in patients with COVID-19 may be due to a cytokine storm, hypoxic injury, endothelial dysfunction, hypercoagulability, and/or increased platelet activity. This study has several limitations. A diagnosis of thrombosis may be underestimated because imaging studies were limited due to concerns of transmitting infection or competing risk of death. Type of MI was not confirmed with cardiac catheterization. Clinical practice changed over the study period, with increased awareness of thrombotic events and use of anticoagulation, which may affect the incidence of thrombosis.