Objective— Endoluminal vascular interventions such as angioplasty initiate a sterile inflammatory response resulting from local tissue damage. This response drives the development of intimal hyperplasia (IH) that, in turn, can lead to arterial occlusion. We hypothesized that the ubiquitous nuclear protein and damage-associated molecular pattern molecule, high-mobility group box 1 (HMGB1), is one of the endogenous mediators that activates processes leading to IH after endoluminal injury to the arterial wall. The aim of this study is to investigate whether approaches that reduce the levels of HMGB1 or inhibit its activity suppresses IH after arterial injury. Approach and Results— Here, we show that HMGB1 regulates IH in a mouse carotid wire injury model. Induced genetic deletion or neutralization of HMGB1 prevents IH, monocyte recruitment, and smooth muscle cell growth factor production after endoluminal carotid artery injury. A specific inhibitor of HMGB1 myeloid differentiation factor 2–toll-like receptor 4 (TLR4) interaction, P5779, also significantly inhibits IH. HMGB1 deletion is mimicked in this model by global deletion of TLR4 and partially replicated by myeloid-specific deletion of TLR4 but not TLR2 or receptor for advanced glycation endproducts deletion. The specific HMGB1 isoform known to activate TLR4 signaling (disulfide HMGB1) stimulates smooth muscle cell to migrate and produce monocyte chemotactic protein 1/CCL2) via TLR4. Macrophages produce smooth muscle cell mitogens in response to disulfide HMGB1 also in a TLR4/myeloid differentiation primary response gene (88)/Trif-dependent manner. Conclusions— These findings place HMGB1 and its receptor, TLR4 as critical regulators of the events that drive the inflammation leading to IH after endoluminal arterial injury and identify this pathway as a possible therapeutic target to limit IH to attenuate damage-associated molecular pattern molecule–mediated vascular inflammatory responses.