The purpose of this article is to review the changing role of the electrocardiogram in the diagnosis of cardiac chamber enlargement. Electrocardiographic criteria for the diagnosis of ventricular hypertrophy and atrial enlargement are reviewed in relation to autopsy, angiographic, echocardiographic and imaging findings. The electrocardiographic theory underlying the recognition of hypertropphy or dilation incorporates a number of sound physical principles that may lead to meaningful correlations with the tissue mass, chamber diameter and intracardiac blood volume. However, there are limiting factors related to the variable orientation of the heart in the chest, variable extracardiac factors and nonspecificity of each depolarization and repolarization abnormality used in the diagnosis of hypertrophy or dilation. This explains the superiority of the new noninvasive methods, in particular echocardiography, in the diagnosis of hypertrophy. Echocardiography is superior to electrocardiography in the detection of mild hypertrophy, and is more useful in the serial follow-up of changes during progression or regression of chamber enlargement.