The main objectives of type 1 diabetes mellitus (DM) management include keeping glycemia levels within the euglycemic range to prevent complications. Daily self-monitoring is an important problem for many diabetic patients, particularly for adolescents. The aim of this study was to evaluate the determinants of poor daily self-monitoring, focusing on the patients' parents' perception of the problem. In order to evaluate parents' awareness of their children's disease-monitoring status, we carried out a cross-sectional investigation of a sample of children and adolescents from a population-based register, with the corresponding population of parents. To collect our data, we used a 33-item questionnaire, separately administered by diabetologists to both parents and children. We estimated the concordance with respect to patients' and parents' answers. Adolescents followed their overall medical prescriptions more regularly (48.8%) than children (29.7%), but most frequently they forgot to use glycemic tests (adolescents 42.4%, children 29.7%). A major duration of disease affected HbA1c levels (values > 8%) of patients younger than 14 years (pFisher = 0.016). Our results indicate a worse compliance of adolescents with respect to children in attending to daily self-monitoring, not just regarding daily glycemic levels but also the course of daily activities such as going to school, studying, working, and simulating symptoms and signs of hypo-hyperglycemia. Parents mostly ignored their child's self-monitoring status and the related motivations.