Background. This study aimed to explore how critical and acceptable practice are defined in anaesthesia and how this influences the discussion and reporting of adverse incidents. Method. We conducted workplace observations of, and interviews with, anaesthetists and anaesthetic staff. Transcripts were analysed qualitatively for recurrent themes and quantitatively for adverse events in anaesthetic process witnessed. We also observed departmental audit meetings and analysed meeting minutes and report forms. Results. The educational value of discussing events was well-recognized; 28 events were discussed at departmental meetings, of which 5 (18%) were presented as ‘critical incidents’. However, only one incident was reported formally. Our observations of anaesthetic practice revealed 103 minor events during the course of over 50 anaesthetic procedures, but none were acknowledged as offering the potential to improve safety, although some were direct violations of ‘acceptable’ practice. Formal reporting appears to be constrained by changing boundaries of what might be considered ‘critical’, by concerns of loss of control over formally reported incidents and by the perception that reporting schemes outside anaesthesia have purposes other than education. Conclusions. Despite clear official definitions of criticality in anaesthesia, there is ambiguity in how these are applied in practice. Many educationally useful events fall outside critical incident reporting schemes. Professional expertise in anaesthesia brings its own implicit safety culture but the reluctance to adopt a more explicit ‘systems approach’ to adverse events may impede further gains in patient safety in anaesthesia.