Introduction: in obese diabetes mellitus 2 (DM2) patients, is difficult conventional medical management for controlling, particulary in those with increased or morbid obesity. In this regard, bariatric surgery has been used in recent years to control DM2 associated to obesity. Objective: To evaluate the impact of bariatric surgery on the improvement of DM2 12 months after surgery. Methodology: A retrospective cohort of obese diabetic patients managed in an Esalud hospital in Lima- Perú was done. The exposed group was subjected to bariatric surgery and the non-exposed group received the conventional treatment. Glycemia and glycosylated hemoglobin (Hbg) were evaluated, before and after the interventions. The effect of the interven-tions on the patients was evaluated. We included 173 obese diabetic patients (41 exposed and 132 unexposed). Cumulative incidences, relative risk (RR), absolute risk reduction (RAR) and relative risk reduction (RRR) were calculated. Results: the most widely used technique of CB was gastric bypass in 27 (67.8%) patients. It was observed that the reduction in median glycosylated hemoglobin and fasting glycemia after bariatric surgery was statistically significant (p<0.01), unlike the unexposed group who showed no change. The annual incidence of DM2 in those exposed was 29.3% (CI95%: 14.1; 44.4) while in the unexposed it was 90.1% (CI95%: 85.6; 96.2), being the RR of DM2 of 0.32 (CI 95%: 0.2; 0.5). The absolute risk reduction (RAR) was 60.8%, and the relative risk reduction (RRR) was 67.8%. Discussion: the results are similar to some studies related to bariatric surgery in obese DM2 patients, in which besides, there were not deaths, no surgical complications and no diabetic foot. Conclusions: The results of the study show that bariatric surgery evidences beneficial effects in patients with DM2 and obesity, as well as the limitations of conventional treatment on this type of patients.