Importance: The prevalence of workplace mistreatment and its association with the well-being of emergency medicine (EM) residents is unclear. More information about the sources of mistreatment might encourage residency leadership to develop and implement more effective strategies to improve professional well-being not only during residency but also throughout the physician's career. Objective: To examine the prevalence, types, and sources of perceived workplace mistreatment during training among EM residents in the US and the association between mistreatment and suicidal ideation. Design, Setting, and Participants: In this survey study conducted from February 25 to 29, 2020, all residents enrolled in EM residencies accredited by the Accreditation Council for Graduate Medical Education (ACGME) who participated in the 2020 American Board of Emergency Medicine computer-based In-training Examination were invited to participate. A multiple-choice, 35-item survey was administered after the examination asking residents to self-report the frequency, sources, and types of mistreatment experienced during residency training and whether they had suicidal thoughts. Main Outcomes and Measures: The types and frequency of workplace mistreatment and the sources of the mistreatment were identified, and rates of self-reported suicidality were obtained. Multivariable logistic regression models were used to examine resident and program characteristics associated with suicidal thoughts. Results: Of 8162 eligible EM residents, 7680 (94.1%) responded to at least 1 question on the survey; 6503 (79.7%) completed the survey in its entirety. A total of 243 ACGME-accredited residency programs participated, and 1 did not. The study cohort included 4768 male residents (62.1%), 2698 female residents (35.1%), 4919 non-Hispanic White residents (64.0%), 2620 residents from other racial/ethnic groups (Alaska Native, American Indian, Asian or Pacific Islander, African American, Mexican American, Native Hawaiian, Puerto Rican, other Hispanic, or mixed or other race) (34.1%), 483 residents who identified as lesbian, gay, bisexual, transgender, queer, or other (LGBTQ+) (6.3%), and 5951 residents who were married or in a relationship (77.5%). Of the total participants, 3463 (45.1%) reported exposure to some type of workplace mistreatment (eg, discrimination, abuse, or harassment) during the most recent academic year. A frequent source of mistreatment was identified as patients and/or patients' families; 1234 respondents (58.7%) reported gender discrimination, 867 (67.5%) racial discrimination, 282 (85.2%) physical abuse, and 723 (69.1%) sexual harassment from patients and/or family members. Suicidal thoughts occurring during the past year were reported by 178 residents (2.5%), with similar prevalence by gender (108 men [2.4%]; 59 women [2.4%]) and race/ethnicity (113 non-Hispanic White residents [2.4%]; 65 residents from other racial/ethnic groups [2.7%]). Conclusions and Relevance: In this survey study, EM residents reported that workplace mistreatment occurred frequently. The findings suggest common sources of mistreatment for which educational interventions may be developed to help ensure resident wellness and career satisfaction.