We report two brothers, aged 22 and 34, affected by dilated cardiomyopathy. At the first examination both patients were in NYHA functional class I. Their echocardiograms showed dilated and hypokinetic ventricles. Their clinical condition remained stable for three years, during which the peripheral immunophenotyping of T-lymphocyte subsets showed T-helper/T-suppressor ratio values lower than normal (normal value for our laboratory = 1.64 +/- 0.53) due both to low T-helper and to high T-suppressor subsets. Subsequently, the clinical condition of both patients deteriorated, exercise tolerance decreased and echocardiographic ventricular diameters increased. T-helper/T-suppressor ratio progressively increased from the initial values of 0.8 and 0.42 to 2.5 and 2.24, respectively. A few months later, both patients died, one because of refractory heart failure and the other one suddenly. Histologic examination of myocardial tissue in one patient showed a diffuse necrotizing disease involving myocytes with focal lymphocyte infiltrates, granulation tissue and endocardial thrombosis. The reported data underline the importance of genetic and familial factors in the pathogenesis and evolution of dilated cardiomyopathies. The increasing T-helper/T-suppressor ratio value which matched the deterioration of the clinical status, is proposed as a useful evolutive and prognostic marker.