Using a one-day prospective point prevalence design, this study aimed to characterise the current practice of mechanical ventilation and weaning in Australian and New Zealand intensive care units. During 2005, a bi-national one-day survey of 55 intensive care units found the point-prevalence of mechanical ventilation to be 284/491(58%). Common modes used were synchronised intermittent mandatory ventilation with pressure support, pressure support ventilation (each 116/284, 41%) and pressure-control modes (48/284, 17%). Relative to volume-control modes, pressure-control was more frequently used for patients with respiratory disease (odds ratio 4.7, 95% confidence interval 2.4 to 9.2, P <0.001) or greater severity of illness (odds ratio 1.7, 95% confidence interval 1.1 to 2.6, P = 0.01, per five-point increment in the maximum sequential organ failure score). Excluding cardiothoracic surgery patients, the Kaplan-Meier estimated median total ventilation duration was 1.9 days (interquartile range 0.8 to 6.8 days). Apart from 24/255 (9.4%) patients who received only pressure support ventilation, weaning methods (attempted in 255 patients, 29 prior deaths) included: change to pressure support ventilation (186/255, 73%), T-piece (31/255, 12%) or other methods (14/255, 5.5%). The point prevalence of mechanical ventilation was greater than comparable international studies. Australian and New Zealand intensive care unit ventilatory practices are similar, but differ substantially from published international survey results, due to a near absence of assist/control, prominent use of pressure-control modes and a preference forpressure support ventilation weaning as opposed to T-piece.