Certain clinical and cardiac necropsy findings are described in 152 patients aged 16 to 78 years (mean 45) with idiopathic dilated cardiomyopathy: 109 (72%) were men and 43 (28%) were women. Compared with the women, the men had a significantly (p less than 0.05) shorter mean duration of chronic congestive heart failure (CHF) (43 vs 69 months), a higher percentage of habitual alcoholism (40 vs 24%) and a higher mean heart weight (632 vs 551 g). The male to female ratio among the 58 known alcoholics was 7.3:1 and among the 70 known nonalcoholics, 1.5:1 (p less than 0.05). The mean duration of clinical evidence of CHF was similar among the known alcoholics and the known non-alcoholics (each 50 months). Of the 152 patients, 148 (97%) had clinical evidence of chronic CHF; in 114 patients it was the initial manifestation of idiopathic dilated cardiomyopathy, and in most it became intractable and caused death. The interval from onset of chronic CHF to death (known in 120 patients) ranged from 1 to 264 months (mean 54). Comparison of the 27 patients surviving greater than 72 months after onset of chronic CHF to the 64 patients surviving less than or equal to 36 months disclosed a significantly higher frequency in the longer survival group of older patients, of women, of habitual alcoholics, of patients with chest pain syndromes, diabetes mellitus, pulmonary emboli, of patients treated with warfarin and of patients with larger hearts at necropsy. Each of the 4 patients without chronic CHF died suddenly and sudden death was the initial manifestation of idiopathic dilated cardiomyopathy in them. An additional 33 patients also died suddenly, but each of them previously had had chronic CHF. Of the 79 patients (of the 131 for whom information was available) with either pulmonary or systemic emboli or both, 67 (85%) had either right- or left-sided thrombi or mural endocardial plaques or both, whereas of the 52 patients without emboli, 36 (69%) had intracardiac thrombi or plaques (p less than (0.05). Electrocardiograms in the last 6 months of life in 101 patients disclosed atrial fibrillation in 25; complete left (41 patients) or right (6 patients) bundle branch block or indeterminate intraventricular conduction delay (4 patients) in 51 patients; QRS voltage indicative of ventricular hypertrophy in 44 patients (left ventricular in 39 patients.(ABSTRACT TRUNCATED AT 400 WORDS)