Idiopathic dilated cardiomyopathy (IDC) is characterized by left ventricular dilatation and systolic dysfunction after known causes have been excluded. Idiopathic dilated cardiomyopathy occurring in families, or familial dilated cardiomyopathy (FDC), may occur in 20% to 50% of IDC cases. Sixteen genes have been shown to cause autosomal dominant FDC, but collectively may account for only a fraction of genetic causation; it is anticipated that additional genes causative of FDC will be discovered. Familial dilated cardiomyopathy demonstrates incomplete penetrance, variable expression, and significant locus and allelic heterogeneity, making clinical and genetic diagnosis complex. Echocardiographic and electrocardiographic screening of first-degree relatives of individuals with IDC and FDC is indicated, as detection and treatment are possible before the onset of advanced symptomatic disease. Genetic counseling for IDC and FDC is also indicated to assist with family evaluations for genetic disease and with the uncertainty and anxiety surrounding the significance of clinical and genetic evaluation. Genetic testing is not yet commonly available, but its emergence will provide new opportunities for presymptomatic diagnosis.