The aim of the study was to evaluate the factors that influence weight regain after Roux-en-Y gastric bypass operation in obese patients. The study included 25 patients who underwent Roux-en-Y gastric bypass operation in 2005-2007 at the Hospital of Lithuanian University of Health Sciences Kaunas Clinics. Patients were evaluated for anthropometric measurements, dietary habits were assessed by 24-hour Dietary Recall and Food Frequency Questionnaires, anxiety and depression disorders were evaluated using Hospital Anxiety and Depression Scale and for physical activity WHO Global Physical Activity Questionnaire was completed by patients. Computed tomography and upper GI endoscopy were utilized to evaluate anatomical factors. A total of 25 patients, aged 49.72 ± 11.03 years, were evaluated. Average time since surgery was 11.80 ± 2.78 years, and the vast majority of study participants were women (88%). Patients in the control group lost maximum 94.77 ± 17.51% EWL and experienced 16.03 ± 12.51% EWL weight regain. The weight regain group reached a maximum of 78.83 ± 24.52% EWL and regained 38.73 ± 18.55% EWL. There was no difference in physical activity between the groups except the time spent sitting: 187.50 ± 130.03 min. in control group and in WR group 338.89 ± 129.47 min. (p = 0.03). All subjects were consuming an insufficient daily amount of protein: 0.69 ± 0.31 g / kg in the control group, 0.51 ± 0.167 g / kg WR group. The WR group consumes more fatty products (58.91 ± 43.72 g) than control group (50.57 ± 24.37 g). There is no difference in dietary habits between groups. In the CT scan, gastric pouch volume was determined: control group average of 17.25 ± 7.86 ml, WR group average of 29.00 ± 17.20 ml, p = 0.076. In the Upper GI endoscopy, the stomach length was determined to be 1.92 ± 0.20 cm in control group and 2.70 ± 1.25 cm in the WR group, p = 0.082. Psychiatric and eating disorders among the groups were distributed without statistically significant difference. A statistically significant factor among the groups was the time spent sitting alone. No differences in nutrition and anatomical factors among groups were found. The incidence of psychiatric and eating disorders among the study groups also did not differ.