It has been suggested that various factors related to dilated cardiomyopathy (DCM) may concern its onset and/or progression. This study was performed to clarify whether these factors contribute different clinical and morphological characteristics. Subjects were 39 patients with DCM, consisting of 28 men and 11 women whose average age was 46.5 years. The subjects were divided into five groups; namely, the Familial, Myocarditic, Alcoholic, Hypertensive, and Unknown Groups. Clinical parameters including past history, blood pressure, chest radiographs, electrocardiograms, echocardiograms and left ventricular end-diastolic pressures (LVEDP) were evaluated. Morphology of right ventricular endomyocardial biopsy specimens was evaluated in terms of hypertrophy, disarrangement, fibrosis, degeneration, endocardial thickening, interstitial changes, and types of fibrosis. The results were as follows: The Familial Group was characterized by the onset at younger age, highly elevated LVEDP, a lack of myocardial hypertrophy, and proliferation of small vessels. The Myocarditic Group was characterized by the onset at young age, elevated LVEDP, severe fibrosis showing a plexiform pattern in more than half of the patients, cellular disarrangement, and cellular infiltration. The Alcoholic Group showed possible improvement clinically and fatty infiltration in half of the patients. The Hypertensive Group was characterized by high prevalence of a previous alcohol intake, high diastolic blood pressure on admission, clinical improvement, and myocardial hypertrophy with a mild degree of perivascular fibrosis. From these findings, it is thought that each factor related to DCM offers a somewhat different clinical and histological profiles and that these factors may play an important role in the onset and/or progression of DCM. Furthermore, it is highly suggestive that specific therapy against these factors or the removal of these factors is especially necessary for favorable long-term prognosis of DCM.