AbstractIdiopathic dilated cardiomyopathy is generally considered a sporadic, nongenetic disorder, and reports of familial cases are often regarded as rare occurrences. Results of the present investigation of 6 families with this disorder suggest that familial forms of dilated cardiomyopathy occur more frequently than previously suspected. The familial nature of the dilated cardiomyopathy was not readily apparent in 3 of these families until thorough family investigations had been performed. The clinical symptoms and age of onset were variable from one family to another and within families. Based on these observations, it is recommended that all persons diagnosed with dilated cardiomyopathy have a thorough review of their family history. If there are any cases of unexplained heart disease, sudden unexpected death or syncopal episodes, further investigations of relatives should be performed. Echocardiography is a convenient noninvasive tool for investigating relatives. Early diagnosis of affected relatives is important for 2 reasons—treatment of significant arrhythmias may prevent sudden unexpected death, and genetic counseling can be provided.