Abstract. Staphylococcus lugdunensis, a very virulent coagulase negative species, has been recently recognized, and rarely reported in few cases, as a cause of endocarditis. This infection, in contrast to the ordinary staphylococcus epidermidis, is frequently lethal and carries a very high risk of devastating embolic complications. In this paper, it was reported that aggressive infection in a child presenting with mitral valve endocarditis, major left cerebral infarction, bulbar palsy and incontinence, with a favorable outcome after combined medical and surgical treatment in King Abdulaziz University Hospital ─ Open Heart Unit. The aim of this report is to emphasize the importance of detailed and advanced microbiological identification of the exact coagulase negative species to avoid overlooking an aggressive pathogen.