The association of hypogonadotropic hypogonadism with anosmia defines Kallmann's syndrome. The gene of the X-linked form of this syndrome has been cloned and several mutations described. However, the relatively small number of hypogonadotropic hypogonadic patients with Kallmann's gene defects supports the hypothesis that other genes may be involved. Idiopathic hypogonadotropic hypogonadism (IHH) is not associated with anosmia. The GnRH gene was excluded as a candidate gene in IHH since no abnormality was found in several patients. The action of the GnRH is mediated through a G-protein coupled receptor present in the cell membrane of gonadotropes. The GnRH receptor was thus another candidate gene. Recently, we described the first patient with partial hypogonadotropic hypogonadism without anosmia caused by loss of function mutations of the GnRH receptor. We compare this first family with a new family presenting complete hypogonadotropic hypogonadism and a variable degree of gonadotrope deficiency in the affected kindred, and discuss genotype-phenotype correlation.