In 30 consecutive hypertrophic cardiomyopathy (HCM) patients who eventually died and 50 who survived, morphologic and functional changes in the heart during a follow-up period of an average of 3.9 years were echocardiographically evaluated. Echocardiographic indices were compared among 5 groups of patients with HCM, consisting of 4 groups of patients who eventually died (SD: 17 patients who suffered sudden death, ED: 4 who died of embolism, HF: 4 who died of congestive heart failure, NC: 5 who died of a noncardiac event) and 1 group of patients who survived with nondilated left ventricle (S: 50 patients). These indices at the last evaluation before death were compared with histopathological findings of left ventricles in 12 autopsied patients. At the initial evaluation ED and HF patients had a larger left ventricular end-diastolic dimension (LVDd), and HF patients had a smaller percent fractional shortening (%FS) and a slower normalized rapid filling rate (nRFR: mean rapid filling rate/LVEDV) than S patients, but these indices showed no differences between SD and S patients. During follow-up, no echocardiographic indices changed in S patients, but LVDd was increased and %FS and nRFR were decreased in SD and HF patients. Mean myocyte diameter and % area of disarray showed no differences among the 4 death groups. However, compared with NC, the other 3 groups, especially HF, had larger % area of massive fibrosis. The % area of massive fibrosis was correlated with LVDd (r = 0.80, p less than 0.005), %FS (r = -0.64, p less than 0.05), and nRFR (r = -0.95, p less than 0.001) at the last evaluation. These results suggested that echocardiographic follow-up was useful in predicting the progression of the myocardial lesion and the prognosis of HCM.