Objective: Managing type 1 diabetes (T1D) requires the ability to make complex and critical decisions regarding treatment, to execute complex tasks accurately, and to make adjustments when problems arise. This requires effective neuropsychological competences of patients and their families, especially in the domain of executive functioning (EF): the ability to self-monitor, plan, solve problems, and set priorities. Previous research focused mainly on child EF, neglecting the impact of parental EF. This study included both mothers and fathers and examined associations between child and parental EF and treatment adherence to T1D in a broad age range of patients. Methods: Parents of 270 patients (6-18years) with T1D (mean age 12.7years; 52.6% female) were included. Mothers (N=232) and fathers (N=168) completed questionnaires on child and parental EF and on treatment adherence. Analyses examined the associations linking child and parental EF to treatment adherence and glycemic control (and potential moderation effects in these associations) using hierarchical linear regression. Results: Child EF problems were negatively associated with treatment adherence. As an indication of moderation, this effect was stronger in older children. Better treatment adherence and glycemic control were reported when both child and parent showed less EF problems. Effects were more pronounced in mothers than in fathers. Conclusions: This study demonstrated a significant interplay between child and parental EF in the association with treatment adherence and glycemic control. Researchers and clinicians should remain attentive toward the role of neuropsychological concepts such as EF. Implementation in clinical practice seems meaningful.