The familial occurrence of hypertrophic cardiomyopathy is well known; familial dilated cardiomyopathy has so far received less attention. Ten families with two or more members affected by dilated cardiomyopathy were studied by echocardiography. In 3 out of 10 families, a transverse study extended to even apparently healthy subjects was carried out, which included a total of 45 subjects. In 19 out of the 45, dilated cardiomyopathy (either symptomatic or asymptomatic) was diagnosed at echocardiography. Three more relatives, already dead of the disease, were identified through hospital records. A clinical and echocardiographic longitudinal study, lasting up to 11 years, was carried out in 5 of the 10 families. During the follow-up, 8 out of 19 patients who, at first examination were affected by dilated cardiomyopathy, died, one improved, 3 remained in stable condition and 7 were lost at follow-up. One of two patients who presented echocardiographic findings suggestive of border-line dilated cardiomyopathy returned to normality and the other developed dilated cardiomyopathy. The clinical and echocardiographic findings in our patients, and in their relatives, suggest the possibility that idiopathic dilated cardiomyopathy may be a multifactorial disease in which genetic factors might play a variable role.