Aim. To evaluate endothelial function (EF) and to estimate the level of a serum apoptosis marker (caspase-8) in patients with metabolic syndrome (MS) and in those with non-alcoholic fatty liver disease (NAFLD). Subjects and methods. The investigation enrolled 76 patients: 43 with MS (out of them, 72.1% were found to have NAFLD) and 33 without MS and NAFLD. All the patients underwent evaluation of EF by photoplethysmography; the level of caspase-8 as one of the apoptosis markers was studied in all. Results. Increased arterial stiffness was more common in a group of patients with MS. Systolic duration was higher in these patients (p<0.05). In these patients, an occlusion test revealed the significantly more marked signs of endothelial dysfunction (ED), which correlated with some cardiovascular diseases (CVD), and hepatic steatosis (p<0.05). The mean level of caspase-8 was significantly higher in the group of MS patients (p<0.05). There was a positive correlation between caspase-8 levels and hepatic and pancreatic steatosis, obesity, aortic atherosclerosis, type 2 diabetes mellitus, and gastroesophageal reflux disease (p<0.05). Conclusion. The study group of MS patients (among whom, there was a preponderance of those with NAFLD) had, firstly, higher arterial stiffness more frequently (as evidenced by photoplethysmography), secondly, longer systolic duration, which may be a risk factor for CVD; thirdly, more pronounced ED. Fourthly, according to the data of a study of caspase-8 levels, its indicator may serve as a prognostic marker for the development of CVD and NAFLD. It was, fifthly, shown that the administration of statins might reduce the degree of apoptosis.