The goal of this research was to investigate whether compensatory beliefs (CBs) regarding glucose testing predict blood glucose levels and adherence to treatment in adolescents with type 1 diabetes. CBs are convictions that the negative effects of one behavior (e.g. not testing one's glucose level) can be compensated for by engaging in another behavior (e.g. not eating any sweets). Adolescent patients from the Diabetes Clinic at the Montreal Children's Hospital and their parents filled out scales while coming for a regular visit. Results from their HbA[subscript 1c] blood test from that visit and prior visits were obtained from their medical records. Results showed that holding glucose testing CBs was associated with poorer HbA[subscript 1c] and poorer adherence to self-care behaviors. Hierarchical regression analyses showed that glucose testing CBs predicted blood glucose control and adherence to treatment above and beyond a number of other constructs including diabetes knowledge. Addressing CBs in diabetes education, in particular targeting those concerning glucose testing, could improve the adherence to treatment and thereby the long-term health of people with diabetes.