Introduction: Ambulance demand in Australia is increasing rapidly. Better understanding of factors influencing ambulance use is fundamental to understanding its use by the public. This has potential to increase appropriate and reduce inappropriate use. Method: Attendances at Adult ED at the MAH in 2002 and 2004 were examined. Predictors of ambulance use were pre-specified as patient demographic and attendance characteristics, clinical acuity, ED diagnosis and patient disposition. Logistic regression was used to derive odds ratios for arrival by ambulance for each predictor variable. Assuming a causal sequence and using logistic regression coefficients, path analyses were derived for three zones: 1) patient demographic and attendance characteristics 2) clinical acuity and likelihood of admission, leading to 3) arrival by ambulance. Results: Higher clinical acuity, greater likelihood of admission, older patients and night time attendances significantly predict ambulance use. Night time arrivals, male and older patients have higher acuity (
