The classical Lesch-Nyhan syndrome has the deficiency of hypoxanthine-guanine phosphoribosyltransferase (HGPRT) activity as the result of mutation in the structural gene for the enzyme located on the X chromosome and is believed to be of X-linked recessive or sex-linked mode of inheritance. This is the first report of a girl who showed typical clinical features and biochemical characteristics of the classical Lesch-Nyhan syndrome. Her mother was not a heterozygote for a deficiency of HGPRT. Possible genetic mechanisms responsible for this case were discussed.