Diabetes mellitus (DM) is a serious medical problem affecting millions of peoples worldwide, and has a great socio-economic impacts. Cytokines possess a pivotal role in modulation of immune reactions and disease pathogenesis. T-helper type 17 (Th17) cells, an important proinflammatory CD4⁺ T cell subset secreting interleukin 17 (IL-17), has been embroiled in development of DM. There are recent evidences supporting a definitive role of Th17 cells in the etiology of type 1 diabetes (T1D). In addition, IL-17 has been shown to play a crucial role in inflammation, insulin resistance, and type 2 diabetes (T2D). Recently, small molecules which have been specified to block Th17 cells differentiation are considered as potential therapeutics for the disease. Anti-IL-17 neutralizing antibodies and/or antibodies targeting Th17 cells have been investigated to protect individuals at risk from disease development. In this review we aimed to shed light on the potential role of IL-17 and Th17 cells in both T1D and T2D pathogenesis and future therapeutic strategies.