Interferon (IFN)-γ has been implicated in restenosis, however its precise role in the pathophysiology of neointimal formation following angioplasty is unclear, as it has been shown to both promote and inhibit neointimal formation. Dietary-induced hypercholesterolemia enhances injury-mediated neointimal formation, associated with increased systemic inflammation and serum IFN-γ. This study examined the effect of IFN-γ gene deficiency ((-/-)) on neointimal formation in a mouse model of endothelial injury combined with an atherogenic diet. Neointimal formation was induced via endoluminal endothelial injury of the common iliac arteries of IFN-γ(-/-) and wild-type (WT) C57Bl/6 mice. Histopathological analysis of the arteries was performed at 3 and 6 weeks post-surgery. IFN-γ(-/-) mice demonstrated a significant reduction in neointimal formation at the 3-week time point, compared to their WT counterpart. No significant differences in plasma lipid profile and the extent of re-endothelialization were detected between IFN-γ(-/-) and WT mice, suggesting that the effect of IFN-γ on neointimal formation is due to injury-mediated vessel neointimal responses. In support of the histopathological findings, immunohistochemical analysis revealed a significant reduction in vessel infiltrating macrophages, and neointimal PDGF-B expression, vascular smooth muscle cell composition and cellular proliferation in the IFN-γ(-/-) mice, in comparison to their corresponding WT group at the 3-week time point. In conclusion, the IFN-γ-mediated pathway plays an important role in inflammatory responses and proliferative effects following injury, suggesting that modulation of the IFN-γ pathway would be beneficial in controlling neointimal formation and restenosis.