Background: Burnout is a psychosocial syndrome, involving feelings of emotional exhaustion, depersonalization, and diminished personal accomplishment at work. Its occurrence is high in healthcare personnel. Job satisfaction is achieved through the feeling of being professionally competent and is an important condition that prevents burnout syndrome. Aim: This study aimed to determine the impact of family physicians' thoughts on self-efficacy of family physician's core competencies on burnout syndrome in Izmir. Subjects and Methods: The study was a nested caseucontrol study and was carried out within the Izmir province from 2013 to 2014. The subject population included 2185 family physicians working in the family medicine centers in the metropolitan districts of Izmir. A total of 395 family physicians who were employed at family medicine centers agreed to participate in the study. After the assessment according to the Maslach Burnout Inventory, 185 physicians had burnout, whereas 210 physicians did not have burnout. Physicians who had burnout were considered as 50% prevalence in the control group; the sampling size was calculated as at least 138 individuals for unpaired cases and control groups, with 0.05 error margin and 80% power. Results: While burnout syndrome was detected in 80.0% of physicians who thought that they were incompetent, it was detected in 30.1% of physicians who believed that they were sufficiently competent in terms of core competencies. Conclusion: Insufficient belief in core competencies by family physicians increases the occurrence of burnout syndrome in these individuals.