Importance: Myocardial injury, detected by elevated plasma troponin levels, has been associated with mortality in patients hospitalized with coronavirus disease 2019 (COVID-19). However, the initial data were reported from single-center or 2-center studies in Chinese populations. Compared with these patients, European and US patients are older, with more comorbidities and higher mortality rates. Objective: To evaluate the prevalence and prognostic value of myocardial injury, detected by elevated plasma troponin levels, in a large population of White Italian patients with COVID-19. Design, Setting, and Participants: This is a multicenter, cross-sectional study enrolling consecutive patients with laboratory-confirmed COVID-19 who were hospitalized in 13 Italian cardiology units from March 1 to April 9, 2020. Patients admitted for acute coronary syndrome were excluded. Elevated troponin levels were defined as values greater than the 99th percentile of normal values. Main Outcomes and Measures: Clinical characteristics and outcomes stratified as elevated or normal cardiac troponin levels at admission, defined as troponin T or troponin I at a level greater than the 99th percentile of normal values. Results: A total of 614 patients with COVID-19 were included in this study (mean age [SD], 67  years; 70.8% male), of whom 148 patients (24.1%) died during the hospitalization. Elevated troponin levels were found in 278 patients (45.3%). These patients were older (mean [SD] age, 64.0 [13.6] years vs 71.3 [12.0] years; P <.001) and had higher prevalence of hypertension (168 patients [50.5%] vs 182 patients [65.9%]; P <.001), heart failure (24 [7.2%]; 63 [22.8%]; P <.001), coronary artery disease (50 [15.0%] vs 87 [31.5%]; P <.001), and atrial fibrillation (33 [9.9%] vs 67 [24.3%]; P <.001). Elevated troponin levels were associated with an increased in-hospital mortality (37% vs 13%; HR, 1.71 [95% CI, 1.13-2.59]; P =.01 via multivariable Cox regression analysis), and this was independent from concomitant cardiac disease. Elevated troponin levels were also associated with a higher risk of in-hospital complications: heart failure (44 patients [19.2%] vs 7 patients [2.9%]; P <.001), sepsis (31 [11.7%] vs 21 [6.4%]; P =.03), acute kidney failure (41 [20.8%] vs 13 [6.2%]; P <.001), multiorgan failure (21 [10.9%] vs 6 [2.9%]; P =.003), pulmonary embolism (27 [9.9%] vs 17 [5.2%]; P =.04), delirium (13 [6.8%] vs 3 [1.5%]; P =.02), and major bleeding (16 [7.0%] vs 4 [1.6%]; P =.008). Conclusions and Relevance: In this multicenter, cross-sectional study of Italian patients with COVID-19, elevated troponin was an independent variable associated with in-hospital mortality and a greater risk of cardiovascular and noncardiovascular complications during a hospitalization for COVID-19.