The human insulin receptor gene is composed of 22 exons and spans in excess of 130 kb, on chromosome 19. The basic structure of the insulin receptor is a disulfide-linked tetramer, composed of the alpha subunit (135 kDa), which is extracellular and provides the binding site for insulin, and the beta subunit (95 kDa), contains the transmembrane domain, tyrosine kinase domain and C-terminal domain. Insulin binding to the alpha subunit causes the activation of the receptor tyrosine kinase activity that plays a critical role in mediating insulin signal transduction. Site-directed mutagenesis or the gene analysis of the patients with insulin resistant diabetes mellitus has revealed the structure and functional relationship of the insulin receptor to some extent but further investigations required.