Background and objectives: Long-term studies exploring factors associated with glycemic control of type 2 diabetes mellitus (T2DM) after bariatric surgery are being requested. This prospective cohort study aimed to evaluate potential predictors of long-term glycemic control 5 years after surgery. Methods: Patients were operated between 2002 and 2014. Data were collected prospectively in a database after obtaining written informed consent from the patients. Surgical methods were sleeve gastrectomy (SG) or biliopancreatic diversion with duodenal switch (BPDDS). Possible predictors of postoperative long-term glycemic control (HbA1c) were investigated using multiple path regression analysis, which handles missing data. Results: A total of 181 patients were included consecutively, 87 after SG and 94 after BPDDS. The follow-up rate was 124/181 (69%), 57 (66%) after SG and 67 (71%) after BPDDS. We found that 39/57 (68%) of the patients who underwent SG and 54/67 (81%) of the patients who underwent BPDDS had remission of T2DM at 5 years. Lower preoperative HbA1c (P < 0.010), higher preoperative C-peptide (P = 0.004), greater percent total weight loss (P < 0.005), and the BPDDS procedure (P < 0.001) were associated with better postoperative long-term glycemic control (explained variance = 39.4%). Conclusions: Both procedures, especially BPDDS, were effective in achieving long-term glycemic control. Lower preoperative HbA1c, higher C-peptide levels, greater weight loss, and the BPDDS procedure were key predictors of better long-term glycemic control.