Aim. To investigate the impact of bariatric surgery (BS) on the level of vitamins in obese patients. Subjects and methods. One hundred obese patients (78 women and 22 men) aged 19 to 61 years were examined. Controlled gastric banding (CGB) was carried out in 20 patients (mean body mass index (BMI), 41.3±8.2 kg/m2); gastric sleeve resection (GSR) in 40 patients, and gastric shunting (GS) in 40 (the mean BMI in these groups were 41.1±17.8 and 45.9±6.2 kg/m2, respectively). A control group consisted of 10 apparently healthy individuals (BMI, 24.9±3.2 kg/m2). An enzyme immunoassay was used to determine the serum concentrations of vitamins В1, В2, В5, В6, В9, В12, С, and D, niacin, biotin, and retinol-binding protein (RBP) before and 1 year after surgery. Results. All the three groups showed a considerable decrease in the levels of vitamins C, В5, В6, and D, and RBP both prior to and following BS. More than 50% of the patients who had undergone GSR had also a lower baseline niacin level. A year after CGB, GSR, and GS, the number of patents with deficiency of these vitamins remained the same or increased. The majority of patients with the same level of vitamin B2, niacin, and folic acid (FA) were observed to have its decrease a year postsurgery. The concentration of the other test vitamins was also reduced a year after all operations; however, it remained within the normal range. GS had no substantial impact on the concentrations of FA, vitamins B2, B12, B1, and biotin. The lower serum vitamin levels were not accompanied by clinical symptoms in most patients following BS. Conclusion. In 80% of the patients with obesity, the levels of vitamins C, B6, and D were decreased to a variable degree. After BS, there was a rise in the number of patients with low serum vitamin C, D, B6, B5, niacin, FA, and RBP concentrations, at the same time the number of patients with FA deficiency increased by more than twice. BS did not significantly affect the metabolism of vitamins В1, В2, В12, and biotin.