Leukotrienes are a group of eicosanoids that are synthesised from arachidonic acid by 5-lipoxygenase (5-LOX) pathway and perform normal and pathological roles. Both leukotriene B4 (LTB4) and cysteinyl leukotrienes (LTC4, LTD4 and LTE4) have membrane receptors. Diabetes mellitus and its complications have complex pathogenic mechanisms, including increased leukotriene synthesis. The implications of leukotrienes and other eicosanoids in the pathogenesis of diabetes are multiple. They are only partially known and frequently completely ignored in medical practice. This review emphasizes the intricate interactions between leukotrienes and other factors in the pathogenesis of diabetes complications. In individuals with diabetes and its complications, the serum and urinary concentration of leukotrienes is significantly higher than in normal individuals. LTB4 and LTC4 inhibit insulin secretion. Leukotrienes are involved in the pathogenesis of diabetic inflammation and stimulate the synthesis of proinflammatory cytokines, in the production of atheromatosis, retinopathy, nephropathy, obesity and various other diabetes complications. Existing data strongly suggest the use of montelukast and other cys-LT1 receptor antagonists in combination with antidiabetic drugs for the treatment of diabetes and its complications. These drugs may prevent or postpone the development of complications of diabetes. This review highlights the involvement of leukotrienes in the pathogenesis of diabetes and its complications. Additionally, various viewpoints on the therapeutic application of leukotriene antagonists are discussed.