Jellyfishes are aquatic organisms, whose number increases under certain conditions of water temperature. They can sting humans, which can be fatal. The liberation of structures known as nematocysts induces the extrusion of the poison, to attack their victims. The poison produces characteristic local and systemic reactions. Since an increased number of these organisms has been detected in our coastline, we review the epidemiology, symptoms and diagnosis of the syndrome produced by the bite, to improve its management (Rev Méd Chile 2004; 132: 233-41)