Research suggests that self-control, the ability to forego immediate needs for the sake of future rewards, promotes health behavior. The present study examined the role of beliefs about willpower as predictor of self-control in the context of diabetes. Seventy-nine type 2 diabetes patients reported their beliefs about willpower, therapy adherence (i.e., self-care activities, diet, exercise), and psychological adjustment (i.e., emotional distress, well-being, life quality). Endorsing the belief that willpower is a lim- ited versus nonlimited resource was associated with lower therapy adherence and lower psychological adjustment. How people think about their willpower might be crucial for therapy success in diabetes patients.