Our purpose in this study was to investigate the correlation of clinical, electrocardiographic, hemodynamic, and histopathologic features at diagnosis with the long-term prognosis in 104 patients with idiopathic dilated cardiomyopathy to determine which factors are the independent determinants of the end-stage disease. During a mean follow-up of 3.8 +/- 3.5 years, 35 patients (33%) died, 14 (13%) suddenly and 21 (20%) from congestive heart failure. Univariate analysis of survival curves disclosed that clinical and electrocardiographic variables at diagnosis were similar in survivors and non-survivors. On the contrary, patients who subsequently died had higher mean right atrial pressure (p = 0.0001), right ventricular end-diastolic pressure (p = 0.0061), mean pulmonary artery pressure (p = 0.0001), and left ventricular systolic (p = 0.0049) and end-diastolic (p = 0.0021) pressure than survivors. They also exhibited larger left ventricular end-diastolic (p = 0.0046) and end-systolic (p = 0.0027) volumes, lower ejection fraction (p = 0.0001), and a greater proportion had severe mitral regurgitation (p = 0.0095). Univariate analysis of histologic findings collected in a subgroup of patients referred since 1984 revealed a mild degree of myocellular hypertrophy to be associated with a poor prognosis (p = 0.0217). Multivariate analysis selected only mean right atrial pressure (p = 0.0022), ejection fraction (p = 0.0089), and end-systolic volume (p = 0.0265) as independent determinants of cardiac death. Our results suggest that cardiac catheterization is mandatory for risk stratification of patients with idiopathic dilated cardiomyopathy, since it allows the assessment of hemodynamic, angiographic, and histopathologic features helpful in identifying patients with a poor prognosis.