Aims: To determine whether the personality traits of conscientiousness and agreeableness are associated with self-care behaviours and glycaemia in Type 2 diabetes. Methods: The Big Five Inventory personality traits Agreeableness, Conscientiousness, Extraversion, Neuroticism and Openness were determined along with a range of other variables in 1313 participants with Type 2 diabetes (mean age 65.8 ± 11.1 years; 52.9% men) undertaking their baseline assessment as part of the community-based longitudinal observational Fremantle Diabetes Study Phase II. Age- and sex-adjusted generalized linear modelling was used to determine whether personality was associated with BMI, smoking, self-monitoring of blood glucose and medication taking. Multivariable regression was used to investigate which traits were independently associated with these self-care behaviours and HbA_1c. Results: Patients with higher conscientiousness were less likely to be obese or smoke, and more likely to perform self-monitoring of blood glucose and take their medications (P ≤ 0.019), with similar independent associations in multivariate models (P ≤ 0.024). HbA_1c was independently associated with younger age, indigenous ethnicity, higher BMI, longer diabetes duration, diabetes treatment, self-monitoring of blood glucose (negatively) and less medication taking (P ≤ 0.009), but no personality trait added to the model. Conclusions: Although there was no independent association between personality traits and HbA_1c, the relationship between high conscientiousness and low BMI and beneficial self-care behaviours suggests an indirect positive effect on glycaemia. Conscientiousness could be augmented by the use of impulse control training as part of diabetes management.