Four patients who appeared to suffer from dilated cardiomyopathy in life were found at autopsy to have had chronic myocarditis (two males and two females, aged 7 to 42 years). Before the appearance of cardiac symptoms, a flu-like illness was observed in two cases and fever in two others. The duration of illness was from 7 months to 10 years and 11 months (mean: 3 years and 8 months) and the heart weight in three adult patients varied from 510 to 940 g (mean: 720 g). Histologic observation of a transverse ventricular section in each patient showed 10 to 187 clusters of small round cells, and massive fibrosis was also found at these sites. The mean percent area of interstitial fibrosis was 26.3% in the ventricular septum, 31.2% in the left ventricular free wall, and 21.6% in the right ventricular free wall. These histologic findings indicated the presence of myocarditis, which was presumably chronic. Our findings suggest that some of the patients diagnosed as having dilated cardiomyopathy may in fact have chronic myocarditis.