This study evaluated population trends in presentations for mental health problems presenting to emergency departments (EDs) in New South Wales during 2010–2014, particularly patients presenting with suicidal ideation, self-harm, or intentional poisoning. Of the 331,493 mental health related presentations, the rate was highest for 15–19 year-old patients, but had grown most rapidly for 10–14 year-old children (13.8% per year). The combined number of presentations for suicidal ideation, self-harm, or intentional poisoning increased in all age groups, other than those aged 0–9 years; the greatest increase was for the 10–19 year-old age group (27% per year). The rate of mental health presentations to EDs increased significantly in NSW between 2010 and 2014, particularly presentations by adolescents with suicidal ideation or self-harm. Urgent action is needed to provide better access to adolescent mental health services in the community and to enhance ED models of mental health care. The underlying drivers of this trend should be investigated to improve mental health care.