Sixty-five patients with dilated cardiomyopathy underwent 24 hour electrocardiographic monitoring: 62 (95.4%) showed ventricular arrhythmias and 52 (80%) complex ventricular arrhythmias (multiform ventricular extrasystoles, paired ventricular extrasystoles and ventricular tachycardia). Complex ventricular arrhythmias correlated significantly with some haemodynamic indices of ventricular dysfunction: patients with multiform and paired ventricular extrasystoles and with ventricular tachycardia had lower values of ejection fraction (31.9 +/- 11.8%, P = 0.002) and of cardiac index (2.9 +/- 0.7 litres/min/m2, P = 0.029) than the others (41.1 11.1% and 3.5 +/- 0.9 litres/min/m2 respectively). Patients were followed for a period of 30 +/- 18 months (20 days to 64 months). During follow-up 19 died and mortality was higher among patients with multiform and paired ventricular extrasystoles and/or ventricular tachycardia. Complex ventricular arrhythmias are frequent in dilated cardiomyopathy: ventricular tachycardia and multiform and paired ventricular extrasystoles seem to be related to a more depressed ventricular function and to a poor prognosis. The importance of antiarrhythmic treatment in these patients has still to be evaluated.