Psoriasis is a chronic inflammatory T cell-mediated immunological disease. It is found to be associated with an increased expression of T-helper 1 and T-helper 17 lymphocytes and decreased expression of T-helper 2 and T-regulatory lymphocytes. Interleukin 10 (IL-10) is an important immunosuppressive cytokine mainly produced by T-helper 2 and T regulatory cells. The main function of IL-10 is to terminate and control inflammatory processes and thereby maintain an immunological homeostasis. Because of its anti-inflammatory properties, IL-10 is a current focus of interest in research. Relative deficiency of IL-10 is found to play the main role in the immunopathogenesis of psoriasis. Analyzing the expression of IL-10 will provide a better understanding of its role in the pathogenesis of psoriasis. Only a few studies have analyzed the role of IL-10 in the pathogenesis of psoriasis, and their findings were contradictory. This article reviews and analyzes the role of IL-10 and its promoter gene polymorphism in the pathogenesis of psoriasis.