Few multi-centre studies of the impact of computerised provider order entry (CPOE) systems on health care efficiency and effectiveness exist. Further, demonstrating a link between system use and improvements in patient outcomes is challenging. An often neglected step is to characterise the nature of the problem prior to CPOE introduction to ensure that the 'problem' being addressed has a demonstrated impact on the outcome of interest. We undertook a two-staged project to i) investigate the link between test turnaround time (TAT) and length of stay for emergency department patients prior to CPOE; ii) to measure the impact of CPOE on TAT in four Australian hospitals to examine the consistency of findings. We found TAT is a significant contributor to length of stay. All four hospitals experienced a significant reduction in TAT following CPOE. This study presents evidence that TAT is directly related to length of stay and that CPOE systems are effective at reducing TAT. These results add weight to the hypothesis that the introduction of CPOE may positively impact upon patient outcomes.