BACKGROUND:Fascial dehiscence (FD) occurs in up to 14.9% of high-risk patients undergoing emergency laparotomy. Although prophylactic mesh can prevent FD, its use in emergency operations remains controversial. STUDY DESIGN:A prospective randomized clinical trial was conducted at the Hospital das Clínicas from Faculdade de Medicina da Universidade de São Paulo in Brazil. It was performed among high-risk patients, defined according to Rotterdam risk model, undergoing midline emergency laparotomy. The patients were randomized into the suture group (SG), with slowly absorbable running sutures placed with a 36-mm-long needle at a suture-to-wound length ratio of 4:1, and the prophylactic mesh group (PMG), with fascial closure as in the SG but reinforced with onlay polypropylene mesh. The primary end point was incidence of FD at 30 days post operation. RESULTS:We analyzed 115 patients; 52 and 63 were allocated to the SG and PMG, respectively. In all, 77.4% of the cases were for colorectal resection. FD occurred in 7 (13.5%) patients in the SG and none in the PMG (p = 0.003). There was no difference between the groups in number of patients with surgical site occurrence (SSO) or SSO requiring procedural intervention. However, some specific SSOs had higher incidences in the mesh group: surgical site infection (20.6% versus 7.7%; p = 0.05), seroma (19.0% versus 5.8%; p = 0.03), and nonhealing incisional wound (23.8% versus 5.8%; p = 0.008). Of SSOs in the PMG and SG, 92.3% and 73.3%, respectively, resolved spontaneously or with bedside interventions. CONCLUSIONS:Prophylactic onlay mesh reinforcement in emergency laparotomy is safe and prevents FD. Surgical site infection, seroma, and nonhealing incisional wound were more common in the mesh group, but associated with low morbidity within 30 days post operation.