Intestinal malrotation is an uncommon finding in adult patients. This finding in candidates to bariatric surgery may conditionate the surgery to be performed. We present a case of a Type IIIA intestinal malrotation in a patient scheduled for a Roux-n-Y Gastric Bypass (RYGB). A 52 years old woman with a BMI 41kg/m2 with no past medical history. A grade B esophagitis in endoscopy was found so she was scheduled for a RYGB. A simplified RYGB was going to be performed as in our usual practice. After constructing the pouch the angle of Treitz was not found and abnormal distribution of the large bowel was observed. Under the suspicion of an intestinal malrotation, an additional trocar was added to look for the ileocecal valve. The Ladd bands and a Type IIIA intestinal malrotation were found. Moving proximal from the ileocecal valve the angle of Treitz was identified and the simplified RYGB was completed. The mesenteric defect was closed, but due to the abnormal distribution of the transverse colon and the small bowel, no Petersen Space was found. Patient did an uneventful postoperatory and was discharge on postoperative day 3. 3 months after surgery she was doing well with an adequate weight loss and no complications.