BACKGROUND: Clinicians and healthcare staff report high levels of burnout. Two common burnout assessments are the Maslach Burnout Inventory (MBI) and a single-item, self-defined burnout measure. Relatively little is known about how the measures compare. OBJECTIVE: To identify the sensitivity, specificity, and concurrent validity of the self-defined burnout measure compared to the more established MBI measure. DESIGN: Cross-sectional survey (November 2016-January 2017). PARTICIPANTS: Four hundred forty-four primary care clinicians and 606 staff from three San Francisco Aarea healthcare systems. MAIN MEASURES: The MBI measure, calculated from a high score on either the emotional exhaustion or cynicism subscale, and a single-item measure of self-defined burnout. Concurrent validity was assessed using a validated, 7-item team culture scale as reported by Willard-Grace et al. (J Am Board Fam Med 27(2):229-38, 2014) and a standard question about workplace atmosphere as reported by Rassolian et al. (JAMA Intern Med 177(7):1036-8, 2017) and Linzer et al. (Ann Intern Med 151(1):28-36, 2009). KEY RESULTS: Similar to other nationally representative burnout estimates, 52% of clinicians (95% CI: 47-57%) and 46% of staff (95% CI: 42-50%) reported high MBI emotional exhaustion or high MBI cynicism. In contrast, 29% of clinicians (95% CI: 25-33%) and 31% of staff (95% CI: 28-35%) reported definitely burning out or more severe symptoms on the self-defined burnout measure. The self-defined measures sensitivity to correctly identify MBI-assessed burnout was 50.4% for clinicians and 58.6% for staff; specificity was 94.7% for clinicians and 92.3% for staff. Area under the receiver operator curve was 0.82 for clinicians and 0.81 for staff. Team culture and atmosphere were significantly associated with both self-defined burnout and the MBI, confirming concurrent validity. CONCLUSIONS: Point estimates of burnout notably differ between the self-defined and MBI measures. Compared to the MBI, the self-defined burnout measure misses half of high-burnout clinicians and more than 40% of high-burnout staff. The self-defined burnout measure has a low response burden, is free to administer, and yields similar associations across two burnout predictors from prior studies. However, the self-defined burnout and MBI measures are not interchangeable.