Atherosclerosis is characterized by frequent communication between infiltrating leukocytes and vascular cells, through chemokine and cytokine networks. IL-17 cytokine family members, including IL-17C, are detectable within atherosclerotic plaques, however the potential involvement of these cytokines have not been examined. Thus we sought to investigate the role of IL-17C in atherosclerosis. The expression of IL-17 cytokines was profiled within atherosclerotic Apoe -/- aortas and Il17c expression was elevated. Flow cytometry experiments revealed a major population of aortic IL-17C-producing smooth muscle cells. To determine the role of IL-17C in atherosclerosis, we generated Il17c -/- Apoe -/- mice and compared atherosclerotic lesions between western diet-fed Apoe -/- and Il17c -/- Apoe -/- mice. Atherosclerotic lesion and collagen content was diminished within WD-fed Il17c -/- Apoe -/- aortas and aortic roots in comparison to Apoe -/- controls, and IL-17C treated Apoe -/- aortas up-regulated Col1A1 expression ex vivo . Flow cytometric analysis of Il17c -/- Apoe -/- aortas revealed a proportional reduction in aortic leukocytes, macrophages, neutrophils, T cells, Th1, and T regulatory cells, without corresponding changes in the peripheral immune composition. Examination of aortic IL-17A + TCRγδ T cells and Th17 cells demonstrated a stark reduction in the percentage and number of these subsets within Il17c -/- Apoe -/- mice versus Apoe -/- controls. Explanted 12 week WD Apoe -/- aortas treated with IL-17C resulted in the induction of multiple vascular chemokines and cytokines, and short-term homing experiments revealed diminished recruitment of Th17 cells to the aorta of Il17c -/- Apoe -/- recipients. Smooth muscle cell-derived IL-17C plays a pro-atherogenic role by supporting the recruitment of Th17 cells to atherosclerotic lesions.