Idiopathic dilated cardiomyopathy (DCM) is a familial disease in at least 20 to 30% of all cases. Knowledge of the genetic basis of familial DCM has been obtained only recently. Mutations in the genes responsible for sarcomere and cytoskeletal protein synthesis have been identified as the cause of DCM, and several hypotheses have been put forward to explain the etiology and pathology of the disease. However, DCM has several causes, and a number of environmental factors influence its course. This review aims to describe the current status of research on familial DCM in the areas of genetics and molecular biology, and to report the clinical applications of this new knowledge. Cooperation between clinical researchers and colleagues in molecular genetics is essential for progress in enhancing our knowledge of this disease.