Newly identified T helper cell 22 (Th22) is a subset of CD4+ T cells with specific properties apart from other known CD4+ T cell subsets. Th22 is obviously discrete from Th17 and Th1 subsets by production of interleukin (IL)-22 but not IL-17 or IFN-γ, and also with distinguished expression of aryl hydrocarbon receptor (AHR) as the key transcription factor. This T helper subset, by producing pro-inflammatory cytokines such as IL-22 and tumor necrosis factor-α (TNF-α), is implicated in the pathogenesis of inflammatory and autoimmune disorder. This review discusses the role of Th22 and its cytokine IL-22 in the immunopathogenesis of autoimmune disease including acute coronary syndrome, psoriasis, atopic dermatitis, rheumatoid arthritis, systemic lupus erythematosus, Behçet's disease, type 1 and 2 diabetes and immune thrombocytopenia.