Labor unions are purported to improve working conditions; however, little evidence exists regarding the effect of resident physician unions. To evaluate the association of resident unions with well-being, educational environment, salary, and benefits among surgical residents in the US. This national cross-sectional survey study was based on a survey administered in January 2019 after the American Board of Surgery In-Training Examination (ABSITE). Clinically active residents at all nonmilitary US general surgery residency programs accredited by the American Council of Graduate Medical Education who completed the 2019 ABSITE were eligible for participation. Data were analyzed from December 5, 2020, to March 16, 2021. Presence of a general surgery resident labor union. Rates of labor union coverage among non-health care employees within a region were used as an instrumental variable (IV) for the presence of a labor union at a residency program. The primary outcome was burnout, which was assessed using a modified version of the abbreviated Maslach Burnout Inventory and was defined as experiencing any symptom of depersonalization or emotional exhaustion at least weekly. Secondary outcomes included suicidality, measures of job satisfaction, duty hour violations, mistreatment, educational environment, salary, and benefits. A total of 5701 residents at 285 programs completed the pertinent survey questions (response rate, 85.6%), of whom 3219 (56.5%) were male, 3779 (66.3%) were White individuals, 449 (7.9%) were of Hispanic ethnicity, 4239 (74.4%) were married or in a relationship, and 1304 (22.9%) had or were expecting children. Among respondents, 690 residents were from 30 unionized programs (10.5% of programs). There was no difference in burnout for residents at unionized vs nonunionized programs (297 [43.0%] vs 2175 [43.4%]; odds ratio [OR], 0.92 [95% CI, 0.75-1.13]; IV difference in probability, 0.15 [95% CI, -0.11 to 0.42]). There were no significant differences in suicidality, job satisfaction, duty hour violations, mistreatment, educational environment, salary, or benefits except that unionized programs more frequently offered 4 weeks instead of 2 to 3 weeks of vacation (27 [93.1%] vs 52 [30.6%]; OR, 19.18 [95% CI, 3.92-93.81]; IV difference in probability, 0.77 [95% CI, 0.09-1.45]) and more frequently offered housing stipends (10 [38.5%] vs 9 [16.1%]; OR, 2.15 [95% CI, 0.58-7.95]; IV difference in probability, 0.62 [95% CI 0.04-1.20]). In this evaluation of surgical residency programs in the US, unionized programs offered improved vacation and housing stipend benefits, but resident unions were not associated with improved burnout, suicidality, job satisfaction, duty hour violations, mistreatment, educational environment, or salary.