Despite increases in the use of emergency department (EDs) for mental health care, there are limited data on whether psychiatric patients disproportionately contribute to ED crowding. We conducted a retrospective analysis using a national database of ED visits in the period 2002–11 to describe trends in median and ninetieth-percentile length-of-stay for patients with psychiatric versus nonpsychiatric primary diagnoses. Psychiatric patients who visited the ED were transferred to another facility at six times the rate of nonpsychiatric patients. Median lengths-of-stay were similar for psychiatric and nonpsychiatric patients among those who were admitted to the hospital (264 versus 269 minutes) but significantly different for those who were admitted for observation (355 versus 279 minutes), transferred (312 versus 195 minutes), or discharged (189 versus 144 minutes). Overall, differences in ED length-of-stay between psychiatric and nonpsychiatric patients did not narrow over time. These findings suggest deficiencies in ED capacity for psychiatric care, which may necessitate improvements in both throughput and alternative models of care.