Objective: Glycemic control varies based on lifestyle factors and stress coping mechanisms, which are influenced by personality. The psychological factors associated with glycemic control have not yet been established in patients with type 2 diabetes mellitus (T2DM). The relationship between a 5-factor model of personality and glycemic control was evaluated in individuals with T2DM. Methods: The subjects were 503 Japanese outpatients with T2DM. Glycated hemoglobin A1c (HbA1c) levels, depressive status, insomnia and personality traits were assessed. Lifestyle factors of the patients, such as habitual alcohol consumption and smoking, were also included in the analyses. ResultsBecause the influence of insulin therapy on HbA1c is so strong, we stratified the patients according to : insulin use. Simple regression analysis showed a significant correlation between HbA1c and neuroticism in patients who did not use insulin. After adjustment for confounders, multiple regression analyses revealed that none of the personality factors, including neuroticism, were found to be associated with HbA1c. Conclusion: These findings suggest that personality traits do not have a large impact on glycemic control. Further studies are required to confirm the relationships between psychological factors and glycemic control using a longitudinal study design.