Although the number of mental health presentations to emergency departments is increasing as a result of the integration of psychiatric services with general services, few studies have explored the characteristics of mental health patients presenting to emergency departments in Australia. This study investigated the characteristics of, and outcomes in relation to, people presenting with a mental health problem to one large metropolitan emergency department. Data were collected from the emergency department's electronic records system for adult patients aged 18-65 years old with an emergency department discharge diagnosis of a mental health disorder, including substance abuse and psychosocial crisis, for two months. Mental health patients totalled 5.3% (n= 290) of adult presentations to the emergency department. Over half were male; mean age 37.4 years; 49% were allocated triage category 3/urgent; 45% arrived by ambulance; 39% were overdosed/intoxicated and 55% received one or more diagnostic investigations. Patients who were intoxicated, those who arrived after hours, or patients admitted to a mental health ward were more likely to wait longer than 8h. Findings are broadly in line with that reported for other Australian studies, although the present findings suggest that patients had significantly more routine investigations and there were higher rates of presentations for 'intoxication'.