['To determine the association of platelet indices with spontaneous echo contrast (SEC) in patients with mitral stenosis.', 'A total of 232 consecutive patients with mitral stenosis who undergoing mitral balloon valvuloplasty were enrolled to the study. Patients were divided into two groups according to the formation of SEC in the left atrium. Group 1: mitral stenosis complicated with SEC; Group 2: mitral stenosis without SEC. Transthoracic echocardiography and transoesophageal echocardiography were performed for each patient. Complete blood counting parameters were measured and all routine biochemical tests were performed. There were 133 patients (mean age 42 ± 11 and 74% female) in the SEC(-) group and 99 patients (mean age 45 ± 10 and 64% female) in the SEC(+) group. Plateletcrit (0.25 ± 0.06 vs. 0.27 ± 0.07, P = 0.043) and mean platelet volume (MPV) levels (9.4 ± 1.1 vs. 10.4 ± 1.2, P < 0.001) were significantly higher in the SEC(+) group. When we divided the SEC(+) patients into four subgroups according to previously reported criteria, MPV levels increased to correlate with the degree of SEC (P < 0.001). At multivariate analysis, MPV levels [odds ratio (OR) 2.365, 95% confidence interval (CI) 1.720-3.251; P < 0.001] and PCT levels (OR 2.699, 95% CI 1.584-4.598; P= 0.033) are independent risk factors of SEC in patients with mitral stenosis.'] Do relationship between platelet indices and spontaneous echo contrast in patients with mitral stenosis?