The American Society of Echocardiography (ASE) has recommended diastolic area length and truncated ellipsoid methods for estimating left ventricular (LV) mass by two-dimensional (2D) echocardiography. The major goals of this retrospective study were to (1) assess the correlation between ASE-recommended 2D and M-mode echo-derived measurements of LV mass, (2) compare the two ASE-recommended 2D echocardiography methods, and (3) compare the echo-derived LV mass with anatomic LV mass. The study included 2D echocardiograms obtained within 30 days of death from 34 patients who subsequently underwent autopsy and 2D echocardiograms of 56 normal subjects. The formula used for measurement of M-mode echo-derived LV mass was LV mass = 0.8 (ASE-cube LV mass) + 0.6 gm. For 2D echo-derived LV mass, the ASE-recommended area length and truncated ellipsoid methods in systole and diastole were used, with and without incorporating the papillary muscles into the myocardial shell. LV mass derived by M-mode echocardiography was comparable to that derived by 2D methods, and it is reasonable to use this technique for normally shaped ventricles. When the papillary muscles were included into the myocardial shell, diastolic 2D methods overestimated autopsy LV mass. Both diastolic area length and truncated ellipsoid methods were comparable to autopsy LV mass. When the papillary muscles were excluded, the systolic area length method showed the best agreement with autopsy LV mass.