Kallmann syndrome is an example of hypogonadism (decreased functioning of the sex hormone-producing glands) caused by a deficiency of gonadotropin-releasing hormone (GnRH), which is created by the hypothalamus. Kallmann syndrome is also known as hypothalamic hypogonadism, familial hypogonadism with anosmia, or hypogonadotropic hypogonadism, reflecting its disease mechanism.

Kallmann syndrome is a form of secondary hypogonadism reflecting the fact the primary cause of the defect in sex hormone production lies within the pituitary and hypothalamus rather than a physical defect of the testes or ovaries themselves.