Dilated cardiomyopathy is a heart muscle disease of unknown aetiology, characterized by left ventricular dilatation and impaired systolic function. Data on the incidence and prevalence of the disease is ambiguous, due to geographic variations, patient selection and the diagnostic criteria adopted. METHODS All the post-mortem and clinical cases observed in a consecutive series of 5252 patients resident in Trieste during the period November 1987-November 1989 were studied. RESULTS Incidence of the disease discovered at autopsy was estimated at 4.5/100,000/year (24 cases), while clinical incidence in the same period was 2.45/100,000/year (13 cases). This is a total incidence of 6.95/100,000 new cases a year. A possible family history of heart muscle disease was found in three patients (12.5%). In 15 patients (62.5%) deaths were due to cardiological complications. Endocardial thickening (P = 0.03), fatty infiltration (P = 0.01) and arterial involvement (P = 0.04) were found more frequently in older patients (> 65 years). CONCLUSIONS The study confirms that dilated cardiomyopathy in Europe has a higher incidence than previously suggested and emphasizes the need for greater diagnostic sensitivity, particularly since pharmacological treatment is now so effective.