In 1992, a long-term project was launched by the German Society for Anaesthesiology and Intensive Care Medicine to render quality comparisons between anaesthesia providers. As one of the first volunteer centres, we established the standardised reporting of perioperative anaesthesia related incidents, events, and complications (IEC) in any routine anaesthetic procedure performed. This present study is aimed to explore the longitudinal stability of IEC recordings in one institution, which should be a prerequisite for valid external comparisons. Methods. The analyses were completed on an adult population of 49945 consecutive anaesthetic procedures with peripheral surgery from July 1992 until December 1996. Attribute quality control charts with monthly samples of an average of 954 anaesthetics were used to assess statistical variability of specific IEC incidences. Results. Average proportions were 20% for moderate IEC, 2.7% for severe IEC, 13% for moderate cardio-vascular IEC, 1.3% for severe cardio-vascular IEC, and 2.4% for respiratory IEC. Moderate IEC proportions showed considerable variability during the study period. A series of excess proportions was probably due to educational activities on documentation discipline. In contrast, clinically severe IEC proportions were rather stable. Stability of cardio-vascular IEC proportions resembled the picture of the overall IEC assessment. Monthly respiratory IEC proportions showed smallest variability during the study period. Discussion. Use of the quality control statistics is suitable to distinguish random from systematic influence on quality indicators. IEC recordings that are not specific in pathophysiologic type or are of low grade of clinical severity, are heavily dependent on systematic documentation features. We assume that peak values, such as in times of optimised documentation discipline, better reflect reality than average values because missing reporting is much more likely than false positives.