Procedural violations (intentional deviations from established protocols) are prone to occur in many occupational settings, with a potentially detrimental effect on quality or safety. They are thought to result from organisational practices and the social characteristics of rule-related behaviour. This study makes use of qualitative methods to investigate the nature and causes of violations in anaesthetic practice. Twenty-three consultant anaesthetists took part in the study, which involved naturalistic observations and semi-structured interviews. Several factors influencing anaesthetic violations were identified. These include the nature of the rule, the anaesthetist (both as an individual and as a professional group) and the situation. Implications for the understanding and management of human reliability issues within an organisation are discussed. This study provides an insight into procedural violations, which pose a threat to organisational safety but are distinct from human errors. The study also demonstrates the value of qualitative methods in ergonomics research. It is of relevance to researchers and practitioners interested in human reliability and error, especially in healthcare.