Arterial cannulation is frequently used in the critical care environment. Literaturefocuses on insertion techniques and complications. This report utilized data from the Australian Incident Monitoring Study (AIMS-ICU) national database to identify common problems and contributing factors associated with the use and maintenance of arterial lines. A review of narratives, keywords and contributing factors yielded 251 reports outlining 376 incidents. Of these, 15% describing line insertion problems, 66% line use and maintenance problems and 19% patient injuries. Inadequate line securing, accidental line dislodgement, incorrect set-up, distal ischaemia and infection featured prominently. As a result of the incident, 49% of patients involved suffered no ill effect, 28% minor physiological complications and 15% suffered major adverse effects. Multiple contributing factors were selected for each report, with lack of knowledge, rule-based errors, high unit activity, and lack of support staff or supervision selected most frequently. This study highlights the need to employ meticulous insertion technique, line set-up, securing, frequent line assessment and the early removal of lines no longer essential to patient care. Support and education of staff as well as the development of protocols are important for the safe use of arterial lines.