Aims: This study was conducted to assess the relationship of simple hematological parameters with the incidence of left atrial thrombus in rheumatic mitral stenosis in addition to conventional contributing factors. Methods: A cross-sectional study was conducted in patients with significant rheumatic stenosis from 1 January 2018 to 31 July 2021. The presence of thrombus was evaluated by transthoracic or transesophageal echocardiography. Laboratory tests were performed within 10 days prior to the echocardiographic evaluation. Subjects with significant mitral regurgitation were excluded. Results: Of the 318 subjects with significant rheumatic mitral stenosis included in the study, 102 patients (32%) had a thrombus in the left atrium. Of all the patients, 63.8% were in atrial fibrillation and 36.2% were in sinus rhythm. Atrial fibrillation (OR 2.39; 95% CI 1.10e5.20, p ¼ 0.028), left ventricular ejection fraction <56.68% (OR 0.42; 95% CI 0.23e0.77, p ¼ 0.005), TAPSE <18.10 mm (OR 0.44; 95% CI 0.230e0.83, p ¼ 0.011), and hematocrit ≥45.15% (OR 2.98; 95% CI 1.27e6.98, p ¼ 0.012) were associated with left atrial thrombus. Conclusion: Increased hematocrit was significantly associated with left atrial thrombus in patients with rheumatic mitral stenosis, which may have contributed to the hypercoagulable state component of the Virchow's triad. © 2023 Hong Kong College of Cardiology.