Hyposmia with hypogonadotropic hypogonadism was diagnosed as Kallmann syndrome in a 24 years old dizygotic female twin. This syndrome indicates the importance of smell in the sexual development through the progenitor cells in the olfactory placode because luteinizing-hormone-releasing hormone (LHRH) secreting cells of hypothalamus arise from these cells. In addition, substitution therapy may be successful in the treatment of the lack of secondary sex traits and primary amenorrhoea as the presented case demonstrated.