Adherence and glycemic control usually decrease during adolescence and family relationships influence diabetes outcomes. This study analyzed the interaction effect of adolescents’ family support, age, and gender in the relationship between adherence and glycemic control in adolescents with Type 1 Diabetes. The sample included 100 adolescents with Type 1 Diabetes and one of their parents during a routine endocrinology appointment. Adolescents answered the Self-Care Inventory—Revised, the Diabetes Family Behavior Scale and were also assessed on the glycosylated hemoglobin. The three-way interaction between adherence, family support, and adolescents’ age/gender was both negatively significant and explained 24.12% and 22.02% of the variance, respectively. Higher family support, being female, and younger age moderated the relationship between adherence and glycemic control. According to results, it is important that intervention programs provide negotiation skills, according to adolescent’s age and gender in the process of transferring diabetes management responsibility in order to promote better adherence to diabetes self-care, glycemic control, and prevent family conflicts regarding diabetes management.