Ten patients with roentgenographically demonstrable mitral annulus calcification (MAC) were found to have distinctive echocardiographic patterns. MAC was confirmed at the time of cardiac catheterization in six of these patients. Standard M-mode echocardiograms revealed a dense band of echoes in the region of the mitral annulus in contrast to the thin and delicate echoes generally recorded from the normal mitral annulus. Intraoperative and pathologic confirmation of thickening and calcification limited to the mitral annulus was made in two patients who underwent mitral valve replacement for severe mitral regurgitation due to myxamatous "floppy" valve. Patients with marked MAC may have coexisting aortic valve or papillary muscle calcification which can be recognized by echocardiography. Over-attenuation of left ventricular wall echoes in patients with marked MAC, and reduction in E-F slope of the anterior mitral valve leaflet in others can simulate pericardial effusion and mitral stenosis, respectively. Thus, recognition of MAC can avoid confusion with similar echocardiographic patterns due to other common cardiac abnormalities.