This narrative review summarizes in vitro, in vivo, and human studies published in English since the discovery of resistin in 2001 to the present, examining the role of this adipokine in the pathophysiology of macrovascular and microvascular complications in in vivo and in vitro T2D models, as well as the clinical evidence supporting its use as a biochemical marker in patients with these conditions. This evidence concerns the gene RETN and type 2 diabetes mellitus.