Dietary trimethylamines, such as choline, metabolized by intestinal microbiota to trimethylamine are absorbed by the gut and oxidized to trimethylamine N-oxide (TMAO). The objective of this study was to determine the effect of choline supplementation on atherosclerosis progression in Apoe^−/− mice expressing human cholesterol ester transfer protein (hCETP) using the same diets as in previously reported studies. Mice expressing hCETP, after transfection with AAV2/8-hCETP, were fed an 18% protein diet with either 0.09% (standard chow), 0.5% or 1% choline for 16 weeks. Control mice not transfected with hCETP were fed 1% choline. Dietary choline supplementation increased plasma TMAO levels at 8 and 16 weeks. When atherosclerotic lesions were measured in the thoracic aorta and aortic root, there were no differences between any of the treatment groups in the amount of plaque development at either site. Throughout the study, no significant changes in plasma lipids or major classes of lipoproteins were observed in hCETP-expressing mice. Plasma-oxidized low density lipoprotein, myeloperoxidase and high density lipoprotein inflammatory index were measured at 16 weeks, with no significant changes in any of these inflammatory markers between the four treatment groups. Despite increasing plasma TMAO levels, dietary choline supplementation in Apoe^−/− mice expressing hCETP did not promote atherosclerosis.