RATIONALE: Burnout syndrome (BOS) associated with stress has been documented in health care professionals in many specialties. The intensive care unit (ICU) is a highly stressful environment. Little is known about BOS in critical care nursing staff. OBJECTIVES: To identify determinants of BOS in critical care nurses. METHODS: We conducted a questionnaire survey in France. Among 278 ICUs contacted for the study, 165 (59.4%) included 2,525 nursing staff members, of whom 2,392 returned questionnaires with complete Maslach Burnout Inventory data. MEASUREMENTS AND MAIN RESULTS: Of the 2,392 respondents (82% female), 80% were nurses, 15% nursing assistants, and 5% head nurses. Severe BOS-related symptoms were identified in 790 (33%) respondents. By multivariate analysis, four domains were associated with severe BOS: (1) personal characteristics, such as age (odds ratio [OR], 0.97/yr; confidence interval [CI], 0.96-0.99; p=0.0008); (2) organizational factors, such as ability to choose days off (OR, 0.69; CI, 0.52-0.91; p=0.009) or participation in an ICU research group (OR, 0.74; CI, 0.56-0.97; p=0.03); (3) quality of working relations (1-10 scale), such as conflicts with patients (OR, 1.96; CI, 1.16-1.30; p=0.01), relationship with head nurse (OR, 0.92/point; CI, 0.86-0.98; p=0.02) or physicians (OR, 0.81; CI, 0.74-0.87; p=0.0001); and (4) end-of-life related factors, such as caring for a dying patient (OR, 1.39; CI, 1.04-1.85; p=0.02), and number of decisions to forego life-sustaining treatments in the last week (OR, 1.14; CI, 1.01-1.29; p=0.04). CONCLUSION: One-third of ICU nursing staff had severe BOS. Areas for improvement identified in our study include conflict prevention, participation in ICU research groups, and better management of end-of-life care. Interventional studies are needed to investigate these potentially preventive strategies.