Psoriasis is a common (1-3% of the population worldwide), multifactorial, immune-mediated chronic skin disease. In psoriasis pathogenesis an over-reaction of local innate immune response initiates inflammation with subsequent involvement of adaptive immune response leading to the production of a panel of cytokines, chemokines and growth factors leading to epidermal hyperplasia. Recently, IL-21 has been involved in this process as this cytokine is overexpressed in psoriatic skin and can cause epidermal hyperplasia and inflammation when injected intradermally into mice. Moreover blockade of IL-21 with a human antibody against IL-21 reduces the epidermal thickness and the expression of Th1 and Th17 genes in the well-characterized model of human psoriasis-xenograft mouse. Therefore, the inhibition of this cytokine may be therapeutically effective in the treatment of psoriasis. Here we will review recent data on psoriasis pathogenesis focusing on the role of IL-21 as novel therapeutic target.