Cardiomyopathy is often found in patients with Duchenne and Becker muscular dystrophy, which are X linked muscle diseases caused by mutations in the dystrophin gene. Dystrophin defects present in many different ways and cases of mild Becker muscular dystrophy have been described in which cardiomyopathy was severe. Female carriers of Duchenne muscular dystrophy can develop symptomatic skeletal myopathy alone or combined with dilated cardiomyopathy. They can also develop dilated cardiomyopathy alone. X linked dilated cardiomyopathy has been found in association with dystrophin defects. The relation between the molecular defects and the cardiac phenotypes has not yet been established. New mutations in the dystrophin gene are common and such mutations cause one third of the cases with Duchenne and Becker muscular dystrophy. This means that sporadic cases of cardiomyopathy caused by dystrophin defects are likely. This paper reports such a case in a boy of 14 who died of dilated cardiomyopathy. Before the cardiac investigation, which was performed one month before he died, he had not complained of muscular weakness. He had minor signs of limb girdle myopathy and slightly increased concentrations of serum creatine kinase. He was found to have an unusual deletion in the dystrophin gene.