Dilated cardiomyopathy (DCM) is the most frequent form of primary myocardial diseases and the third most common cause of heart failure. Clinically, DCM is characterized by a progressive course of ventricular dilatation and systolic dysfunction. The life expectancy is limited and varies according to the underlying etiology with a median survival time of about 5 years after diagnosis. Myocarditis, immunologic abnormalities, toxic myocardial damage, and genetic factors are all assumed to be causes. Familial occurrence of DCM, mostly as an autosomal dominant trait, is more common than generally believed and is responsible for 20-30% of all cases of DCM. Candidate gene screening and linkage analyses in large families were successful in identifying 24 disease genes. There is a wide variability in the onset, course and severity of the disease even within the same family. In addition, genotype-phenotype correlations included only small numbers of affected. This implies that in most cases no conclusion can be drawn from the clinical manifestation of DCM to the responsible disease gene. Mutations in the beta-myosin heavy chain and in cardiac troponin T are common causes of pure familial DCM. DCM associated with conduction disease is mainly due to mutations in lamin A/C and X-linked DCM is often caused by mutations in dystrophin. All other disease genes are rare causes of familial DCM. Genetic screening in all known disease genes is not possible, but more efficient screening methods are awaited in the near future. Until then, clinical examination of family members and, in case of familial DCM, genetic counseling are recommended in the work-up of patients with idiopathic DCM.