Endurance sports such as marathon running are increasingly popular, attracting both professional and recreational athletes. While most participants recognize that these events can result in health hazards, few consider death a likely outcome. Exercise associated hyponatremia can be a consequence for which fatal outcomes may occur. In some it is mild and without symptoms. However, in others it is of such severity that respiratory failure secondary to pulmonary edema, and possibly death may result. This article reviews new information regarding predisposing factors, treatment, and outcomes associated with exercise induced hyponatremia and the Varon-Ayus syndrome (hyponatremia, pulmonary edema and cerebral edema associated to marathon running).