The prevalence of mediastinal masses in large-scale populations in China has been rarely reported. During COVID19 pandemic, many incidentalomas were reported due to the large amount of chest computed tomography scan performed in emergency setting.Retrospective analysis of emergency chest computed tomography scans (February 2020- February 2021) for COVID-19 screening, including mediastinal abnormalities (excluding lymph nodes, dysplasia, pneumomediastinum and other non-mass alterations), with computed tomography features, diagnostic workup and 1 year follow-up data were reviewed.Of the 40,112 patients (mean age 54.5 (17.2) years; male-to-female ratio 1.02:1) screened for COVID-19, 293 (0.73%) had mediastinal masses of which 223 (0.56%) located in the anterior mediastinum. As participants aged, the prevalence tended to increase (P < 0.001). The prevalence was not different between the sexes (P = 0.635). An oval shape, anterior mediastinal location, and thymus involvement were the most common computed tomography characteristics. Surgery confirmed 11.3% (33 of 293) of nodal lesions, with a benign to malignant ratio of 51.4: 48.5. A computed tomography scan follow-up was conducted in 32.3% (84/260) of the patients, and in 82.1% (69/84) of cases the lesion was stable. Additionally, mediastinal masses were detected in 7.7% (20/260) of elderly patients who passed away soon after their primary disease worsened.In Chinese COVID-19 screening chest computed tomography, the prevalence of all mediastinal masses and anterior mediastinal masses was 0.73% and 0.56%, respectively. Findings support risk-stratified management: growing/suspicious lesions warrant intervention versus surveillance for stable masses. Standardized protocols and multidisciplinary consensus are critical.© The Author(s) 2025. Published by Oxford University Press on behalf of the European Association for Cardio-Thoracic Surgery.