BACKGROUND Postoperative nausea and vomiting are relevant complications after restrictive bariatric procedures, such as sleeve gastrectomy, mainly secondary to a drastic reduction in the gastric volume. However, other causes can be involved. The aim of this study was to determine the incidence of postoperative nausea and vomiting (PONV) after laparoscopic sleeve gastrectomy (LSG), with staple line reinforcement with oversewing vs buttressing material. METHODS A prospective randomized clinical trial of all the patients undergoing LSG was performed. Patients were divided into 2 groups: patients undergoing staple line inversion (Group 1) and patients undergoing staple line reinforcement with buttressing material (Group 2). Nausea and vomiting were assessed by the Postoperative Nausea and Vomiting Intensity Scale. RESULTS A total of 100 females were included in the study, 50 in each group. Mean operative time was 66.1 ± 11.6 min in Group 1 and 55.4 ± 9.4 in Group 2 (p < 0.001). There were no significant differences in staple line leaks and bleeds between groups. The PONV intensity score at 6 h was 316.4 in Group 1 and 77.1 in Group 2 (p < 0.001). 24 h after surgery, the PONV intensity score was 86 in Group 1 and 7.9 in Group 2 (p = 0.022). CONCLUSIONS The reinforcement with a running suture in LSG creates more PONV and increases the duration of the symptoms during the first hours after surgery, and prevents from early oral intake in a greater number of cases, when compared with the use of buttressing material as reinforcement method.