Background: The aim of this study was to assess left ventricular (LV) function and the Tei index by tissue Doppler imaging (TDI), and also to evaluate the relationship of serum cortisol level with the Tei index and LV function in patients with Cushing's Syndrome (CS). Methods: We prospectively evaluated 22 patients with CS and 23 control subjects. LV function was assessed by echocardiography. Early diastolic (Em), late diastolic (Am), peak systolic (Sm), mitral annular velocities, Em/Am, the Tei index, and E/Em were calculated by TDI. Mitral inflow velocities, color M-mode flow propagation velocity (Vp), relative wall thickness (RWT), and LV mass index (LVMI) were assessed by two-dimensional echocardiography. Result: Peak (E) velocity and the ratio of E to peak late (A) velocity (E/A) were lower in those with CS than in those without. Patients with CS had significantly higher RWT, IVRT, and LVMI than those controls. Vp was lower in the CS-patients than that in control subjects. Em and Em/Am were lower in patients with CS than those in controls. In patients with CS, the Tei index was significantly higher than control subjects. Conclusion: Serum cortisol level was positively correlated with the Tei index and E/Em ratio but negatively correlated with Em, Sm, and EF only in patients with CS. Serum cortisol level positively correlated with the Tei index and E/Em ratio but negatively correlated with Em, EF, and Sm. The parameters obtained from lateral mitral annulus by TDI can be used for identification of LV diastolic dysfunction in patients with CS.