Here, we report a case of 21-OHD due to a new variant of cluster mutation of p.[Ile237Lys; Val238Glu; Met240Lys] on the CYP21A2 gene, located in the long arm of chromosome 6 in a Japanese woman. Here, CYP21A2 is linked to classic congenital adrenal hyperplasia due to 21-hydroxylase deficiency.