The CXC ligand (CXCL)12/CXC receptor (CXCR)4 chemokine–receptor axis controls hematopoiesis, organ development, and angiogenesis, but its role in the inflammatory pathogenesis of atherosclerosis is unknown. Here we show that interference with Cxcl12/Cxcr4 by a small-molecule antagonist, genetic Cxcr4 deficiency, or lentiviral transduction with Cxcr4 degrakine in bone marrow chimeras aggravated diet-induced atherosclerosis in apolipoprotein E-deficient (Apoe^−/−) or LDL receptor–deficient (Ldlr^−/−) mice. Chronic blockade of Cxcr4 caused leukocytosis and an expansion of neutrophils and increased neutrophil content in plaques, associated with apoptosis and a proinflammatory phenotype. Whereas circulating neutrophils were recruited to atherosclerotic lesions, depletion of neutrophils reduced plaque formation and prevented its exacerbation after blocking Cxcr4. Disrupting Cxcl12/Cxcr4 thus promotes lesion formation through deranged neutrophil homeostasis, indicating that Cxcl12/Cxcr4 controls the important contribution of neutrophils to atherogenesis in mice