OBJECTIVE: We aimed to determine the midterm effect of a ketogenic diet on serum lipid levels, carotid intima-media thickness, and the elastic properties of the carotid artery and the aorta in patients with intractable epilepsy. METHODS: A total of 52 children aged between 12 months and 18 years with intractable epilepsy who started the ketogenic diet from September 2014 to September 2015 were included into this prospective study. Carotid intima-media thickness and the elastic properties of the carotid artery and the aorta were assessed by echocardiography in all cases before beginning of the ketogenic diet and after at least 12 months on the ketogenic diet. RESULTS: Twenty-one patients at the third month and 25 patients at the first year of the ketogenic diet were seizure free. A reduction of greater than 90% in the seizure frequency was achieved in three patients at the sixth month and in five patients at the first year of the treatment. The serum levels of total cholesterol, low-density lipoprotein, and triglyceride were increased significantly at a median of 12.6 months (range: 12 to 13.5 months) of the ketogenic diet treatment, whereas serum levels of high-density lipoprotein did not change. Carotid intima-media thickness, aortic and carotid strain, the stiffness index, distensibility, and elastic modulus did not change after 12 months of the ketogenic diet therapy. CONCLUSION: Olive oil-based ketogenic diet appears to have no disturbing effect on the carotid intima-media thickness and the elastic properties of the aorta and the carotid artery in epileptic children, although it may be associated with increased concentrations of serum lipids.