Dilated cardiomyopathy (DCM) is one of the leading causes of heart failure. Several prospective studies have shown that about 25-30% of all cases are of familial etiology. The most common mode of inheritance is autosomal dominant. Less frequently is inheritance as an X-chromosomal trait. Examination of families has identified nine disease genes so far. The penetrance of the identified mutations is highly variable and age-dependent. Many relatives of patients with DCM show only minor cardiac abnormalities, and it is unknown whether they progress to full cardiomyopathy in later life. Knowledge of the DCM disease genes led to the new hypothesis that DCM is a disease of myocardial generation or transmission of force. Better understanding of the expression and function of disease genes may lead to new diagnostic and therapeutic tools.