Objectives:The objective of this study was to describe demographic and clinical characteristics includingfeatures that were consistent with subarachnoid hemorrhage (SAH), use of diagnostic tests, emergencydepartment (ED) discharge diagnoses, and disposition of adult patients presenting with an acute headache toEDs statewide across Queensland, Australia. In addition, potential variations in the presentation and diagnosticworkup between principal-referral and city-regional hospitals were examined.Methods: A prospective cross-sectional study was conducted over 4 weeks in September 2014. All patients ≥ 18years presenting to one of 29 public and five private hospital EDs across the state with an acute headache wereincluded. The headache had to be the principal presenting complaint and nontraumatic. The 34 study sites attend toabout 90% of all ED presentations statewide. The treating doctor collected clinical information at the time of the EDvisit including the characteristics of the headache and investigations performed. A study coordinator retrievedresults of investigations, ED discharge diagnoses, and disposition from state databases. Variations in presentation,investigations, and diagnosis between city-regional and principal-referral hospitals were examined.Results: There were 847 headache presentations. Median (range) age was 39 (18–92) years, 62% were female,and 31% arrived by ambulance. Headache peaked instantly in 18% and ≤ 1 hour in 44%. It was “worst ever” in37%, 10/10 in severity in 23%, and associated with physical activity in 7.4%. Glasgow Coma Scale scorewas < 15 in 4.1%. Neck stiffness was noted on examination in 4.8%. Neurologic deficit persisting in the ED wasfound in 6.5%. A computed tomography (CT) head scan was performed in 38% (318/841, 95% CI = 35% to41%) and an lumbar puncture in 4.7% (39/832, 95% CI = 3.4% to 6.3%). There were 18 SAH, sixintraparenchymal hemorrhages, one subdural hematoma, one newly diagnosed brain metastasis, and twobacterial meningitis. Migraine was diagnosed in 23% and “primary headache not further specified” in 45%. CThead scans were more likely to be performed in principal-referral hospitals (41%) compared to city-regional hospitals (33%). The headache in patients presenting to the latter was less likely to be instantly peaking orassociated with activity, but was no less severe in intensity and was more frequently accompanied by nauseaand vomiting. Their diagnosis was more likely to be a benign primary headache. Variations in CT scanning couldthus be due to differences in the case mix. The median (interquartile range) ED length of stay was 3.1 (2.2 to 4.5)hours. Patients was discharged from the ED or admitted to the ED short-stay unit prior to discharge in 57 and23% of cases, respectively.Conclusions: The majority of patients had a benign diagnosis, with intracranial hemorrhage and bacterialmeningitis accounting for only 3% of the diagnoses. There are variations in the proportion of patients receivingCT head scans between city-regional and principal-referral hospitals. As 38% of headache presentations overallunderwent CT scanning, there is scope to rationalize diagnostic testing to rule out life-threatening conditions.