Lesch-Nyhan syndrome (LNS) is a disorder caused by congenital absence of a purine metabolic enzyme, hypoxanthine guanine phosphoribosyl-transferase (HGPRT). This syndrome is characterized clinically by hyperuricemia and neurologic features including choreoathetoid spasticity, self-mutilation, and mental retardation. We report on a patient in whom self-mutilation of the lower lip was suppressed with the help of a mouth guard made from soft resin.