In Japan, the increasing frequency of mental health problems in postgraduate dental trainees has recently become apparent. To our knowledge, there has been no previous research to investigate the inluence of the type of training program on the mental health of dental residents during one year of postgraduate clinical training. Therefore, the purpose of this study was to compare changes in the mental health of two groups of dental trainees at Kyushu University Hospital, Fukuoka, Japan: those who undertook a rotation training program and those who trained solely in one department (the control group). Study subjects in both groups completed the Proile of Mood States (POMS) and the General Health Questionnaire (GHQ) at ive intervals throughout the postgraduate training year. Analysis of the questionnaire responses were performed by Student's t-test, analysis of variance, Bonferroni's test, and the chi-square test. Statistical tests showed differences in the mean scores of POMS-30 subscales and GHQ-28. The mood of anger was the factor that seemed to best describe the trainees' response to stress. The study results led to the conclusion that dental trainees' mental health is inluenced by the type of training program and that dental trainees in rotation training programs may need more mental health support.