This study examined how Dutch type 1 and type 2 diabetes patients’ perceived autonomy support, as well as their perceived competence and treatment self-regulation, are associated with their diabetes self-care activities (healthy diet, physical activity, monitoring blood glucose, medication use) and general diabetes control. A cross-sectional questionnaire study was conducted among 143 type 1 diabetics and 384 type 2 diabetics. Overall, participants felt competent, supported in their autonomy, and perceived to autonomously self-regulate their diabetes. Our results underline the importance of perceived competence in type 1 and 2 diabetics, as this was strongly associated with adhering to a healthy diet and general diabetes control. Our findings also emphasize the need for autonomy supportive health care professionals in diabetes care. Interestingly, perceived competence partially mediated the influence of autonomy support on general diabetes control.