Significance To date, the importance of liver X receptors (LXRs) in atherosclerosis development has been gleaned from their pharmacological or genetic manipulation. Here, we show that altering LXRα phosphorylation can shape proatherogenic responses to fat-rich diets, uncovering previously unrecognized mechanisms. Disrupting LXRα phosphorylation in myeloid cells triggers global changes in gene expression in macrophages, including the up-regulation of proliferation-promoting factors, consistent with increased proliferation of lesion-resident cells. This leads to an enhanced atherosclerotic plaque burden and plaques with altered phenotypic features. Notably, novel LXRα-regulated targets revealed by impaired LXRα phosphorylation are markedly distinct from those promoted by LXR ligand activation. Overall, this work reveals LXRα phosphorylation as an important determinant of atherosclerosis development. This could be exploited for the design of novel antiatherosclerotic strategies.