Xerodermapigmentosum (XP), is an autosomal recessivegenetic disorder of DNA repair in which the ability to repair damage caused by ultraviolet (UV) light is deficient. The oxidative stress caused by decline catalase activity as an antioxidant enzyme, has been illustrated in these patients. This is the first case report of dilated cardiomyopathy in two patients with XP, A 26 year old girl and her younger brother. Laboratory studies demonstrated severe vitamin D deficiency in both of them. Cardiac dysfunction in the presented cases with XP might be caused by vitamin D deficiency. But this question still remains: whether chronic oxidative stress can involve the heart and can be a predisposing factor or even an underlying factor for dilated cardiomyopathy in XP, or not. More studies are needed for demonstrating this hypothesis.