Objective: Identify the incidence of Petersen's hernia in gastric bypass patients at our institution. Summary: Laparoscopic gastric bypass has proved to be the best treatment for obesity and the resolution of their complications, however, it presents long-term complications such as Petersen's hernia. Methods: A retrospective study of a single center, with a total of 225 gastric bypass performed in the bariatric and metabolic surgery clinic of the Hospital Civil de Guadalajara “Dr. Juan I. Menchaca” from January 2014 to March 2020. Results: Of the 225 operated patients, a global follow-up of 80.44% was obtained, with an average postoperative follow-up of 31 (+/-20.92) months, it was found that in 10 patients (4.44%) presented a symptomatic internal hernia. Of these, 9 patients was admitted to the emergency room and 1 detected in the outpatient clinic. These patients presented at the time of surgery a BMI of 27.65 (+/- 5.01) with a percentage of excess weight lost of 62.35% (+/- 25.60). The laparoscopic approach could be completed in 100% of the cases. Regarding hospital stay, an average of 1.1 (+/- 0.31) days was presented. No trans-surgical complications or mortality were reported in the group studied. The mean time between primary surgery and reoperation was 21.3 (+/- 12.98) months. Conclusion: In a 6-year period with a global follow-up of 80.44%, where the Petersen defect was not closed. An incidence of 4.44% was found, with an average follow-up of 31 (+/- 20.92) months. However, the percentage of Petersen's hernia may be underestimated since only those with symptoms that lead the patient to emergency care are usually diagnosed, so a high index of suspicion must always be had.