Objective: Successfully managing Type 1 diabetes involves adherence to a complex daily medical regimen, requiring self-regulatory skills that rely on neurocognitive processes known as executive functioning (EF). Adolescents with poorer rated EF abilities display poorer diabetes outcomes. The purpose of this study was to examine the relationship of EF questionnaire and performance measures with adherence and glycemic control, after controlling for IQ and general questionnaire response style. Method: Adolescents with Type 1 diabetes (M age = 17.74, SD = .38 years) and their mothers (N = 196) completed a self/mother-report questionnaire assessing adolescents’ ratings of EF abilities (Behavior Rating Inventory of Executive Functioning—Self-Report). Adolescents also completed performance-based tests of EF (Delis-Kaplan Executive Function System) and intellectual functioning (Wechsler Adult Intelligence Scale, 4th ed., Vocabulary). Adherence was indexed via 2 self-report inventories and the number of daily blood glucose checks, and glycemic control via HbA1c obtained from assay kits. Results: Self/mother-reports of EF ability were associated with self/mother-reported adherence. Both questionnaire and performance-based measures of EF were associated with glycemic control. However, once IQ was taken into consideration, performance-based EF was no longer associated with glycemic control; IQ independently shared variance with glycemic control. Conclusion: Our findings suggest that self-reports of EF may be useful in identifying late adolescents who need assistance in managing diabetes in daily life. The finding that performance-based EF measures were not related to glycemic control independent of underlying intellectual capacity raises questions about the specific role of EF in diabetes outcomes.