Psoriasis is a chronic, recurrent, inflammatory skin disease that is often accompanied by obesity. An increasing amount of research has elucidated the pathophysiological link between psoriasis and obesity. Since 2005, interleukin (IL)-17-producing T helper 17 cells and their main effector cytokine IL-17A have been considered to play a critical role in the pathogenesis of psoriasis; the marked effect of biotherapies targeting IL-17A on moderate and severe psoriasis has further established its role in psoriasis. Recent studies have found that obesity induces T helper 17 cells to secrete IL-17A and participate in the pathogenesis of psoriasis. IL-17A may be a crucial element in the association between psoriasis and obesity. This review discusses the association between psoriasis and obesity, with a focus on and the implications regarding the need to treat psoriasis.