Examine trends in mental health-related emergency department (ED) visits, changes in disposition and length of stay (LOS), describe disposition by age and estimate proportion of ED treatment hours dedicated to mental health-related visits.

Retrospective analysis of ED encounters in the National Hospital Ambulatory Medical Care Visit Survey with a mental health primary, secondary or tertiary discharge diagnosis from 2009 to 2015. We report survey-weighted estimates of the number and proportion of ED visits that were mental health-related and disposition by age and survey year. We estimate the proportion of ED treatment hours dedicated to mental health-related visits. We analyze trends in disposition and LOS for mental health and non-mental health-related visits using multivariate regression analysis.

Mental health-related ED visits increased by 56.4% for pediatric patients and 40.8% for adults, accounting for over 10% of ED visits by 15–64 year-olds and nearly 9% by 10–14 year-olds in 2015. Mental health-related visit disposition of admission or transfer declined from 29.8% to 20.4% (p < .001); predicted median ED LOS for admissions or transfers increased from 6.5 to 9.0 hours while median LOS for discharges was stable at 4.4 hours. During the study period, mental health-related visits accounted for 5.0% (95% CI 4.6–5.3) of all pediatric and 11.1% (95% CI 11.0–11.3) of adult ED treatment hours.

Mental health-related visits account for an increasing proportion of ED visits and a considerable proportion of treatment hours. A decreasing proportion of mental health-related visits resulted in inpatient disposition and ED LOS increased for admissions and transfers.