Within Australia nursing unions are pursuing mandated nurse-patient ratios to safeguard patient outcomes and protect their members in healthcare systems where demand perpetually exceeds supply. Establishing ratios for an emergency department is more contentious than for hospital wards. The study's aim was to estimate average staffing levels, skill mix and patient presentations in all New South Wales (NSW) Emergency Departments (EDs).The design was a retrospective historical census audit. Nurse rosters and patient presentation data were collected for three randomly selected census days in May 2010. Twenty-six valid responses out of 44 were returned. A ratio of the number of beds per nurse was calculated as well as skill mix and bed occupancy.The average beds per nurse ratios found were 3.8 (morning shift), 3.6 (evening), and 5.1 (night). However, ratios as high as 8.4 (morning), 7.3 (evening) and 16.0 (night) were identified on particular shifts. Overall a rich skill mix was found with an average of 90% of nursing hours being provided by Registered Nurses. The average daily bed occupancy of 4 patients per bed was similar across ED levels.The study adds to the limited literature on ED staffing and demonstrates the utility in the simplicity of ratios in flagging potential staffing problems. The audit revealed wide variation in staffing levels which was not always linked to patient activity. Of particular concern were the regional EDs (Level 5) which have the capacity to deal with all types of emergencies but where ratios as high as 7 beds per nurse were found during the day. Ratios cannot be used to determine the optimal staffing levels in every clinical situation; their purpose is to force an increase in nursing supply and to prevent individual units from becoming understaffed.