Lesch-Nyhan syndrome (LNS) is an X-linked recessive disorder with no racial differences. It occurs in approximately 1 in 100,000 male births, but there are few reports of its occurrence in girls 1) . This is attributed to a single congenital deficiency of the hypoxanthine-guanine phosphoribosyltransferase (HPRT). Most patients die by the age of 40 years due to renal failure or respiratory complications 2,3) . The main symptoms are hyperuricemia, involuntary movements, psychomotor retardation, and self-injurious behavior (SIB) 4) . It is often difficult to control SIB, which is a characteristic symptom of this disease. Although patients appear to develop normally for some time after birth, psychomotor retardation may occur as early as several months after birth, and SIB may appear at around one year of age and may persist into adolescence. Bites on the tongue, lips, and fingers are often a problem, and sometimes tissue loss, insufficiency, or complete amputation may occur 5) . Generally, medicine or orthosis is created to control it. However, when ineffective, surgical treatment is required. We encountered a case in which the tongue and lip ulceration were caused by SIB, which became a gateway to invasion and infective endocarditis (IE). IE is a fatal condition, and considering the possibility of recurrence, total tooth extraction and tongue reduction were performed. There have been no reports of cases of IE developing from SIB in the past. We report the case including a review of the literature.