Congenital hypogonadotropic hypogonadism is defined by reduced steroid hormone synthesis and secretion due to low LH and FSH secretion. It is a rare disease with an unknown prevalence (about 1/5000). It results from a fetal defect in GnRH neuron migration, a defect of pituitary development or from a functional defect of the hypothalamopituitary axis between GnRH neurons and gonadotropic cells. The diagnosis should be considered at birth in males with micropenis, during adolescence in case of delayed puberty or absent puberty, and during adulthood in case of infertility. It may be restricted to the gonadotropic axis, combined with other endocrine system defects or be part of a complex syndrome. Several gene defects have now been described. Molecular studies should be performed to confirm the diagnosis and to help provide appropriate genetic counseling. Treatment to induce puberty should be provided at adolescence, followed by hormonal substitution treatment during adulthood. Specific infertility treatment may also be proposed but patients with the dominant form of gonadotropic deficiency should be informed of the risk of transmission.