Hypogonadotropic hypogonadism 1 with or without anosmia is a disorder characterized by delayed or absent puberty, low levels of circulating gonadotropins and testosterone, and no other abnormalities of the hypothalamic-pituitary axis. It can be caused by a defect in gonadotropin-releasing hormone (GNRH) release or action. Anosmia, cleft palate, and sensorineural hearing loss may be associated non-reproductive phenotypes. Anosmia is linked to the absence or hypoplasia of the olfactory bulbs and tracts. In the presence of anosmia, it is known as Kallmann syndrome, while with a normal sense of smell, it is normosmic idiopathic hypogonadotropic hypogonadism (nIHH). The disorder is inherited in an X-linked recessive manner and is due to genetic changes in the KAL1 gene. Hypothalamic disorders result from a deficiency in the release of gonadotropic releasing hormone (GnRH), while pituitary gland disorders are due to a deficiency in the release of gonadotropins from the anterior pituitary. The central regulator in reproductive function is GnRH, which acts on the gonads for proper adult reproductive physiology.