Background: Diabetes self-management education (DSME) is generally considered to be a key determinant of the treatment outcomes and related costs of diabetes mellitus. While DSME programmes generally have positive outcomes, their effects may depend on certain factors, such as the type of programmes provided and patients' level of health literacy (HL). Low HL has been associated with poorer self-management behaviours and poor medication adherence in diabetic patients, but its impact on the effects of DSME has not yet been systematically investigated. This study aimed to investigate the influence of HL on the self-reported effects of DSME programmes while taking the type of programme into consideration. Method: A total of 366 diabetic patients from nine countries completed a questionnaire measuring HL, self-management behaviours, problem perception, coping, perceived general health and well-being, before and after participating in a DSME programme. Results: DSME programmes were found to have positive effects on self-reported self-management behaviours and almost all psychological and health outcomes, regardless of HL level. Patients with high HL scored better on several diabetes outcomes than those with low HL, but all patients described benefiting from DSME. Individual and group-based programmes resulted in more positive effects on several diabetes outcomes than self-help groups, but no interaction with HL was found. Conclusion: Our findings confirm those of previous studies showing that DSME programmes have positive effects and that low HL is associated with lower diabetes outcomes but do not support the assumption that the effects of DSME programmes are influenced by the patient's HL. However, due to the limitations of this study, further investigation is necessary to support these findings and improve our understanding about the impact of HL on DSME programmes' effectiveness.