The growth hormone (GH)-releasing hormone (GHRH) receptor (GHRHR) belongs to the G protein-coupled receptor family. It binds GHRH resulting in somatotroph cell proliferation and stimulation of GH secretion. Mutations in the gene encoding for GHRHR (GHRHR, OMIM No. 139191) are being reported with increasing frequency in familial isolated GH deficiency. To date, the reported GHRHR mutations include eight missense, seven splice, three microdeletions, and two non-sense mutations. One promoter mutation has also been reported. Most of these mutations show a recessive mode of inheritance. The phenotype includes reduced but not absent serum GH, with abnormal response to a variety of stimuli, and low serum insulin-like growth factor-1 levels, resulting in proportionate growth failure which becomes evident in the first year of life. These patients respond well to GH replacement therapy. Phenotypical observations coming from some unusually large kindreds with untreated GH deficiency due to homozygous GHRHR mutations have allowed the study of the consequences of lifetime lack of GH. This chapter reviews the structure and the role of the GHRHR together with the clinical aspects associated with its mutations.