Objective The objective of this study was to examine temporal trends in mental health visits to the emergency department (ED) and to determine differences in length of stay (LOS) between mental health visits and visits for non-mental health conditions.Methods A population-based retrospective study was conducted for patients who visited the ED of an academic hospital located in Toronto, ON, between fiscal years 2012 and 2016. Trends in the number of visits and descriptive statistics were calculated for both mental health and non-mental health groups. Quantile regression was used to compare the median and 90th percentile LOS.Results In five years, the absolute increase in the number of mental health visits to the ED was 55.7%. The 90th percentile LOS was similar for mental and non-mental health visits that were internally transferred (10.7 hours v. 8.3 hours) but significantly higher for those who were discharged (11.4 hours v. 7.3 hours), admitted (52.6 hours v. 29.3 hours), and externally transferred (21.9 hours v. 10.0 hours). After adjusting for other variables, the 90th percentile LOS was 3.3 hours longer for mental health visits resulting in discharge (p<0.001), 24.5 hours longer for those admitted (p<0.001), and 12.7 hours longer for those externally transferred (p<0.001).Conclusion The number of mental health visits to the ED is linearly increasing over time, and the LOS in the ED is significantly longer for mental health visits for almost all discharge dispositions. Thus, systematic changes are needed to address the ED capacity to provide care for the growing mental health population.