This descriptive, cross-sectional and correlational study aimed to assess the self-care competencies of senior citizens with diabetes using the Scale to Identify Diabetes Mellitus Patients' Competence for Self-Care and personal factors associated with it. The study population consisted of seniors registered in primary healthcare units in Fortaleza, CE, Brazil. Only 6% of the patients were considered to have diabetes self-care competence. Low educational level and decreased visual acuity were identified as factors that influenced these low scores. The results, which showed that a small number of seniors were considered competent to practice self-care, indicated the importance of developing health promotion activities targeted to this population, assessing skills and encouraging self-care practices to facilitate the planning of health interventions.