This study aims to investigate weight regain and the associated variables 10 years after Roux-en-Y gastric bypass. This retrospective study recruited patients submitted to Roux-en-Y gastric bypass (N = 166) for a 10-year follow-up. The following variables were investigated: body mass index (BMI), percentage of excess weight loss (%EWL), weight regain (WR), and percentage of weight regain (%WG). The chi-squared test or Fisher's exact test compared proportions, and the Mann-Whitney test compared numerical measurements between the groups. Analysis of variance (ANOVA) compared the measurements over time. The significance level was set at 5 %. The sample had a mean age of 39.59 +/- 11.69 years, and females prevailed (71.7 %). In the long-term follow-up, 41 % of the patients had weight regain. Seventy-two months after surgery, excess weight, preoperative BMI, gender, age, nutritional monitoring, and iron deficiency did not explain weight regain. Younger patients had regained significantly more weight 96 (p = 0.008) and 120 months (p = 0.004) after surgery than older patients. Patients who regained weight had ferritin < 15 mu g/dL 96 months after surgery (p = 0.019). Patients submitted to Roux-en-Y gastric bypass presented weight regain, which increased over time. Age, iron deficiency, and time since surgery were associated with weight regain in the long-term follow-up.