The goal of this observational study is to explore the experience of the chronic disease, with a particular focus on self-care, in adults with type 2 diabetes mellitus. The main questions it aims to answer are: * what is the association between self-care and glycated hemoglobin over time? * what are participants' clinical and sociodemographic characteristics influencing self-care behaviors? Participants' socio-demographic and clinical data will be collected by medical records and, at the beginning or at the end of the clinical standard outpatient visit, they will be asked to complete study questionnaires. The results of this study could be helpful in providing quality assistance, improving resource consumption, and reducing the onset of complications.