There were 65 incidents involving access to the vascular system amongst the first 2000 reported to the Australian Incident Monitoring Study. Thirty-three involved peripheral venous access (14 cases of extravascular extravasation, 8 of unintended arterial cannulation, 6 of disruptions to intravenous lines, and 5 of problems with infusion lines, taps, pumps and connectors). Eighteen cases involved central venous access (9 cases of arterial puncture with haematomas, 5 with morbidity and/or prolonged admission), 5 of catheter misplacement and pneumo- or hydro-thorax and 4 of problems arising from operator inexperience. Thirteen cases involved peripheral arterial access (5 involved equipment problems (3 with possible air embolism), 3 of mistaking an arterial for a venous line (drugs were injected in 2), 3 of losing arterial lines or signals, and 2 in which the presence of an arterial line placed the patient at risk). The anaesthetist should always question the continued integrity of any vascular access system, even when it has recently been shown to be functioning, and the possibility of later "migration" and misplacement should always be borne in mind. Whenever possible, correct placement of the tip should be checked (e.g. by visual inspection of the site, use of test doses, aspiration of blood, pressure measurement, X-rays). When there is more than one line, all lines and sites of access (e.g. 3-way taps) should be clearly labelled and checked before anything is injected or infused.