Intra- and postoperative adverse events (iAEs and pAEs) occur in up to one third of all patients undergoing surgery. They are devastating to patients and costly to health care systems. Their number tends to increase due to the rising complexity of both the patient's risk profile and the surgical procedure. Postoperative deaths have been identified to be the third most frequent cause of death worldwide. Teamwork in surgery has been attributed to have a potentially great impact on avoiding postoperative morbidity. Up to 50% of all adverse in-hospital events were rated to be potentially preventable. However, their prevention typically requires a change in systems and individual behaviour. Standardised assessments of iAEs and pAEs are a prerequisite to develop and define strategies for prevention of AEs. While awareness of pAEs has highly risen through the introduction of the Clavien-Dindo classification, the most widely used classification for grading severity of pAEs, the relevance of transparent monitoring of iAEs is still highly undervalued.