OBJECTIVE: To determine how residents relationships with their sources of social support (ie, family, friends, and colleagues) affect levels of burnout and loneliness. DESIGN: Cross-sectional survey. SETTING: Faculty of Medicine at the University of British Columbia in Vancouver. PARTICIPANTS: A total of 198 physician-trainees in the universitys postgraduate medical education program. MAIN OUTCOME MEASURES: Residents personal and work-related burnout scores (measured using items from the Copenhagen Burnout Inventory); loneliness (measured using a 3-item loneliness scale); and social support (assessed with the Lubben Social Network Scale, version 6). RESULTS: Of the 234 respondents who completed the Internet-based survey (a 22% response rate), 198 provided complete information on all study variables and thus constituted the analytic sample. Seemingly unrelated regression analyses indicated that loneliness was significantly (P < .01) and positively associated with both personal and work-related burnout scores. Greater friend-based and colleague-based social support were both indirectly associated with lower personal and work-related burnout scores through their negative associations with loneliness. CONCLUSION: Social relationships might help residents mitigate the deleterious effects of burnout. By promoting interventions that stabilize and nurture social relationships, hospitals and universities can potentially help promote resident resilience and well-being and, in turn, improve patient care.