Objective To identify the patient and case characteristics associated with emergency department (ED) suitability of cases referred for emergency ambulance dispatch following ambulance-based secondary telephone triage. Methods A retrospective cohort analysis was conducted of secondary telephone triage cases transported to an ED by emergency ambulance between September 2009 and June 2012 in Melbourne, Australia. Patients were considered ED suitable if they were triaged as a category 1, 2 or 3 according to the Australian Triage Scale, were admitted to hospital or referred to another hospital for admission, or died in the ED. Descriptive statistics and multivariable binary logistic regression analysis were used to identify the variables associated with ED suitability. Results There were 2694 (21.2%) cases classified as ‘not ED suitable’. The mean age of this group was 51.7 years (SD 23.7 years) and 56.5% were female. Those that were ED suitable were older, with a mean age of 59.1 years (SD 22.6 years) and 53.6% were female. After adjusting for confounders the age (p<0.001), pain (p<0.001) and triage guideline groups (p<0.001) variables had statistically significant relationships with ED suitability. Gender (p=0.108), time of day (p=0.118), secondary triage call-taker qualification (p=0.237) and comorbidities (p=0.182) showed no association with ED suitability, and income status was approaching significance (95% CI 0.85–1.02, p=0.055). Conclusion There are patient and case characteristics associated with ED suitability that could be used to improve patient triage to better match patients with care pathways appropriate to their needs.