Objective: To correlate functional capacity and self-care in older adults with diabetes. Method: A cross-sectional and quantitative study, carried out with 189 older adults with diabetes mellitus treated at an endocrinology outpatient clinic. The structured instrument to obtain sociodemographic and clinical data, the Barthel Index, and the Diabetes Self-Care Activities Questionnaire were used. Data was analyzed with descriptive and inferential statistics. Results: Most of the older adults were independent and had high mean values of adherence to self-care. There was a positive correlation with statistical significance between functional capacity and the domains of self-care activities related to physical activity and care with the feet. Conclusions: Functional capacity showed a positive relationship with items related to physical activity and care with the feet. Functional independence in the older adult can influence adherence to self-care practices facing diabetes mellitus.