Physician burnout is a serious issue, given its associations with physician attrition, mental and physical health, and self-reported medical errors. Burnout is typically measured in health care by assessing the frequency of symptoms in 2 domains, emotional exhaustion and depersonalization. However, the lack of a clinically diagnostic threshold to define burnout has led to considerable variability in reported burnout rates. To estimate the prevalence of burnout using a range of definitions (ie, requiring symptoms in both domains or just 1) and thresholds (ie, requiring symptoms to occur weekly vs a few times per year) and examine the strength of the association of various definitions of burnout with suicidal thoughts and thoughts of attrition among general surgery residents. A cross-sectional national survey of clinically active US general surgery residents administered in conjunction with the 2019 American Board of Surgery In-Training Examination assessed burnout symptoms, thoughts of attrition, and suicidal thoughts during the past year. Multivariable logistic regression models were used to assess the association of burnout symptoms with thoughts of attrition and suicidal thoughts. Values of R2 and C statistic were used to evaluate multivariable model performance. Burnout was evaluated with a 6-item, modified, abbreviated Maslach Burnout Inventory for 2 burnout domains: emotional exhaustion and depersonalization. The primary outcome was prevalence of burnout. Secondary outcomes were thoughts of attrition and suicidal thoughts within the past year. Among 6956 residents (a 85.6% response rate; including 3968 men [57.0%] and 4041 non-Hispanic White individuals [58.1%]) from 301 surgical residency programs, 2329 (38.6%) reported at least weekly symptoms of emotional exhaustion, and 1389 (23.1%) reported at least weekly depersonalization symptoms. Using the most common definition, 2607 general surgery residents (43.2%) reported weekly burnout symptoms on either subscale. Subtle changes in the definition of burnout selected resulted in prevalence estimates varying widely from 3.2% (159 residents; most stringent: daily symptoms on both subscales) to 91.4% (5521 residents; least stringent: symptoms a few times per year on either subscale). In multivariable models, all measures of higher burnout symptoms were associated with increased thoughts of attrition (depersonalization: R2, 0.097; C statistic, 0.717; emotional exhaustion: R2, 0.137; C statistic, 0.758; both: R2, 0.138; C statistic, 0.761) and suicidal thoughts (depersonalization: R2, 0.077; C statistic, 0.718; emotional exhaustion: R2, 0.102; C statistic, 0.750; both: R2, 0.106; C statistic, 0.751) among general surgery residents (all P < .001). In a national evaluation of general surgery residents, prevalence estimates of burnout varied considerably, depending on the burnout definition selected. Frequent burnout symptoms were strongly associated with both thoughts of attrition and suicide, regardless of the threshold selected. Future research on burnout should explicitly include a clear description and rationale for the burnout definition used.