Objectives: The aims of this study were to investigate the dentists’ job-related stress using the newly developed Dentist Job Stress (DJS) questionnaire, and to explore the relationships among sociodemographic factors, job stress and mental health indicators, including psychosocial stress, depression, anxiety and sleep among Korean dentists. Materials and methods: An online survey including 1,520 dentists was conducted using the Brief Encounter Psychological Instrument-Korean version (BEPSI-K), the Center for Epidemiologic Studies Depression Scale (CES-D), the State-Trait Anxiety Index (STAI) and the Pittsburgh Sleep Quality Index (PSQI). Results: The response rate was 15.2% (n = 231). The DJS questionnaire consisted of environmental and vocational factors, and Cronbach’s α coefficient was 0.69. Dentists’ job stress was significantly associated with income (P = 0.0230), work time (P = 0.0009) and job satisfaction (P < 0.0001). A bivariate correlation study revealed that the BEPSI-K, CES-D, STAI-S and PSQI exhibited a significant correlation with the DJS scale. Multiple regression analysis found that depression, job satisfaction and sleep quality were associated with dentists’ job stress, and this model accounted for 37.9% of the variation in the DJS scale (P < 0.0001). Conclusions: The findings of this study revealed that the DJS questionnaire showed acceptable validity and reliability, and dentists’ job stress was associated with depression, job satisfaction and sleep quality. The major implication of this study is that a stress-management programme focusing on practical ways to improve the mental health status and job satisfaction of dentists is critical to the reduction of occupational stress among Korean dentists.