The COVID-19 pandemic has raised concerns about the negative impact of the fear of contagion on people's willingness to seek medical care and the subsequent effects on patients' prognosis . To date, not much is known about the outcomes of acute surgical diseases in this scenario . The aim of this multicenter observational study is to explore the effects of COVID-19 outbreak on the outcomes of patients who underwent surgery for peritonitis. Patients undergoing surgery for secondary peritonitis during the first COVID-19 surge in Italy (March 23-May 4, 2020-COVID period group) were compared with patients who underwent surgery during the same time interval of year 2019 (no-COVID period group). The primary endpoint was the development of postoperative complications . Logistic regression analysis was conducted to identify predictors of complications . Of the 332 patients studied, 149 were in the COVID period group and 183 were in the no-COVID period group . Patients in the COVID period group had an increased frequency of late presentations to the emergency departments (43% vs. 31.1% ; P = 0.026) and a higher rate of postoperative complications (35.6% vs. 18% ; P <0.001). The same results were found in the subset analysis of patients with severe peritonitis at surgical exploration . The ASA score, severity of peritonitis, qSOFA score, diagnosis other than appendicitis, and COVID period resulted independent predictors of complications . During the COVID-19 pandemic patients with peritonitis had a higher rate of complicated postoperative courses, weighing on hospital costs and assistance efforts already pressured by the ongoing sanitary crisis.