Objective: To identify any significant differences in the population of patients brought in to a hospital ED under involuntary mental health orders, based on whether the orders are initiated by police or health professionals. Methods: A retrospective analysis of consecutive presentations to a tertiary hospital ED with a co-located psychiatric emergency care centre over a 12 month period, with univariate and multivariate statistical comparisons. Results: Two hundred and eighty-two patients (making 378 ED presentations) met the case definition and were analysed. Compared with patients on medical orders, patients on police orders had significantly more presentations related to violence, longer stays in ED and lower rates of admission to an inpatient bed, but were no more likely to require restraint or security intervention within the ED. Conclusions: Patients on police and medical orders differ considerably, but the impact of these differences on ED workload is small.