Kallmann syndrome is a genetic disorder characterized by idiopathic hypogonadotrophic hypogonadism and anosmia/hyposmia. The X-linked form of Kallmann syndrome is due to the mutation of the KAL1 gene. It encodes a glycoprotein, anosmin-1, which is involved in the embryonic migration of GnRH-synthesizing neurons and the differentiation of the olfactory bulbs. We report a case of a 14-year-old boy who was referred to our endocrinologic clinic for the evaluation of hypogonadism and whose father was anosmic and has been in medication of testosterone for hypogonadism. This boy had a micropenis and small testes (2/2cc) but no neurological manifestations, including mental retardation or mirror movements were observed. The hormonal assay was consistent with hypogonadotrophic hypogonadism. We performed the olfactometry and he was proved to be hyposmic. In the brain MRI, no remarkable olfactory bulb was shown , supporting the clinical diagnosis of Kallmann syndrome. Sequence analysis of KAL-1 gene (Xp22.31) revealed an Adenine deletion (del1521A) in exon 11. His father had a same mutation and this mutation was not found in the normal group. He is in treatment of testosterone replacement. Our report suggests that this novel mutation is responsible for Kallmann syndrome and related with the important area of the anosmin-1. More survey is needed considering the possibility that this mutation may be more prevalent in Korean patients .