This study examined disparities in emergency department (ED) wait time for patients with mental health and substance-related disorders (PwMHSDs), using data from the 2009–2011 National Hospital Ambulatory Medical Care Survey (NHAMCS). Wait time was defined as the time between arrival at ED and being seen by an ED provider. Results from multivariable regression models show racial disparities, with non-Hispanic Black PwMHSDs experiencing longer ED wait time, compared to non-Hispanic White PwMHSDs. A temporal decline in ED wait time was also observed over the study period. The findings of this study have implications for informing the development of policies tailored at facilitating the delivery of equitable emergency care services to all PwMHSDs.