Sixty-nine patients with hypertrophic cardiomyopathy were followed up for a minimum period of 10 years, with detailed quantitation of myocardial hypertrophy using two-dimensional echocardiography at a two-year interval. The parameters determined included maximum myocardial wall thickness, mean myocardial wall thickness (defined as the arithmetic mean of myocardial wall thickness values measured in ten areas of approximately the same size the LV and septal myocardium had been divided into), and the extent of hypertrophy (percentage of the myocardium affected by hypertrophy). Other echocardiographic parameters as well as clinical, ECG and Holter data were also assessed. Seven patients (10%) showed a gradual increase in mean myocardial wall thickness (associated with an increase in maximum myocardial wall thickness and in the extent of hypertrophy in two). By contrast, a progressive decrease in hypertrophy was observed in six patients (9%). In either case, the observed changes tended to involve areas in segments outside the zone of maximum wall thickness. Generally, the changes in hypertrophy were not related to the development of clinical or Holter manifestations, and were unaffected by verapamil or beta-blocker therapy. There was no death among these patients unlike the five deaths in a group with stationary hypertrophy. Based on their results, the authors conclude that changes in myocardial hypertrophy (regardless of whether there is progression or regression) probably make part of natural variations in the course of the disease, and have no clinical or prognostic implications for the majority of patients.