AIM: To compare self-care competencies in the physical, cognitive and emotional and motivational dimensions of patients with diabetes mellitus before and after participation in an educational programme. BACKGROUND: Diabetes mellitus is mainly characterised by a dysfunction of glucose metabolism. The growth of diabetes mellitus as a chronic condition requires continuous management and requires health services to implement care strategies. Diabetes education and self-care competence have been recognised over the last few decades as essential for patients with diabetes mellitus to achieve positive treatment results. DESIGN: A prospective, comparative study was used. METHODS: A total of patients with 43 diabetes mellitus participated in this study, before and after a four-month educational programme on diabetes held in Ribeirão Preto, SP, Brazil in 2009. Data were collected through the Scale to Identify diabetes mellitus Patients' Self-Care Competence [Escala para Identificação da Competência do Portador de diabetes mellitus para o Autocuidado] at two points in time: at the beginning (T1) and at the end (T2) of the programme. Linear mixed effects models were used (p<0·05) in the analysis. RESULTS: Statistically significant differences were not found in relation to physical competence in the comparison between T1 and T2. Statistically significant differences were found in the comparison of cognitive and emotional and motivational competencies, respectively, between T1 and T2. CONCLUSION: The scores related to cognitive and emotional and motivational competencies for self-care presented statistically significant differences between T1 and T2. RELEVANCE TO CLINICAL PRACTICE: The educational activities implemented in the educational programme favoured improved cognitive, emotional and motivational competence for the incorporation of positive self-care actions.