Clinical recognition of hypertensive cardiac involvement depends primarily on use of noninvasive methods. The performance of 8 electrocardiographic (ECG) criteria sets were compared with an echocardiographic standard in the Treatment of Mild Hypertension Study. Electrocardiograms were computer processed to define the following ECG criteria sets: (1) Casale/Devereux, (2) Cornell product, (3) Cornell voltage, (4) 12-lead volt, age product, (5) sum of 12-lead voltage, (6) Rautaharju, (7) Sokolow-Lyon, and (8) Romhilt-Estes. Echocardiographic left ventricular (LV) mass index was calculated by using the Penn convention on a biracial population of 834 men and women. Correlations between ECG and echocardiographic LV mass index were modest (<0.40). ECG-LV hypertrophy sensitivity at 95% specificity was <34%. The Casale/Devereux ECG criteria showed the highest average sensitivity (17%) at 95% specificity for all race-sex groups. Whites had significantly higher correlation values than blacks. ECG correlations with LV mass index were consistently improved by including systolic blood pressure and body mass index. ECG criteria sets appear to be optimized for white men. The study findings confirm the poor ECG sensitivity and correlation with echocardiographic LV mass and suggest: (1) further refinement of ECG criteria alone in white men is unlikely to improve its relationship with LV mass; and (2) combining the electrocardiogram with other non-ECG variables or noninvasive measurements offers the best strategy for improving ECG sensitivity and its prognostic value.