The role of the pro-inflammatory cytokine IL-17 in the pathogenesis of numerous inflammatory disorders is well-documented, but conflicting results are reported for its role in diabetic nephropathy. Here we examined the role of IL-17 signalling in a model of streptozotocin-induced diabetic nephropathy through IL-17 knockout mice, administration of neutralising monoclonal anti-IL-17 antibody and in vitro examination of gene expression of renal tubular cells and podocytes under high glucose conditions with or without recombinant IL-17. IL-17 deficient mice were protected against progression of diabetic nephropathy, exhibiting reduced albuminuria, glomerular damage, macrophage accumulation and renal fibrosis at 12 weeks and 24 weeks. Administration of anti-IL-17 monoclonal antibody to diabetic wild-type mice was similarly protective. IL-17 deficiency also attenuated up-regulation of pro-inflammatory and pro-fibrotic genes including IL-6, TNF-α, CCL2, CXCL10 and TGF-β in diabetic kidneys. In vitro co-stimulation with recombinant IL-17 and high glucose were synergistic in increasing the expression of pro-inflammatory genes in both cultured renal tubular cells and podocytes. We conclude that absence of IL-17 signalling is protective against streptozotocin-induced diabetic nephropathy, thus implying a pro-inflammatory role of IL-17 in its pathogenesis. Targeting the IL-17 axis may represent a novel therapeutic approach in the treatment of this disorder.