 In 6 centres in Switzerland and 13 centres abroad, 2500 consecutive patients undergoing any type of inpatient surgery will be included in this prospective international multicentre cohort study. The primary endpoint corresponds to the risk-adjusted association between the most severe intraoperative complication classified according to CLASSIC and the most severe postoperative complication classified according to the most commonly used classification of postoperative complications developed by Clavien and Dindo. All observed patient-related intraoperative complications between skin incision and closure are considered as intraoperative complications. 