Correlation between pathologically proved mitral ring calcification (MRC) and M-mode echocardiographic findings was examined. Subjects for this study were 36 aged autopsy cases of MRC (14 men, 22 women) with a mean age of 78.9 years. Echocardiographic diagnosis of MRC was based upon the following criteria; a dense echo that moves parallel to the endocardium of the left ventricular posterior wall, immediately posterior to the mitral leaflet and its abrupt termination during a sweep of the beam to the left atrium and left ventricle. The length along the mitral ring and its maximal cross-sectional diameter of MRC were measured pathologically. Extension of MRC to the mitral commissures was also evaluated. The following results were obtained; (1) The larger was the size of MRC measured pathologically, the more it was easily diagnosed by echocardiography. (2) The width of MRC in the echocardiogram correlated well with the pathologically measured maximal cross-sectional diameter of MRC (r = 0.67, p less than 0.01). (3) Sensitivity in the diagnosis of MRC was better in the echocardiograms (58.3%) than in the plain chest X-ray films (38.9%) (p less than 0.05). The length of MRC equal to or greater than 30 mm was diagnosed in all by the echocardiograms. In contrast, only 78.6% of these were diagnosed by plain X-ray films. (4) When cases with MRC were divided into 2 groups according to the mitral diastolic descent rate (MDDR), the decreased group (MDDR less than 35 mm) had a significantly longer length of MRC (32.4 +/- 15.5 mm) than the non-decreased group (16.6 +/- 20.9 mm) (p less than 0.05). Extension of MRC to the mitral commissures was more frequently observed in the group with decreased MDDR than in non-decreased group (p less than 0.005). From these observations, it was suggested that mechanical restriction of the movement of the anterior mitral; leaflet due to involvement of the commissures by MRC may be a contributing factor for decreased MDDR. (5) Identification of echoes from the posterior mitral leaflet and the left ventricular posterior wall was difficult in cases with positive MRC echoes.