Objective –To test the hypothesis that poorer adherence to diabetes care is related to four variables associated with self-concept in adolescents with diabetes: self-esteem, self-efficacy, depression, and binging behavior. In addition, we expected adolescent females to be less adherent to diabetes care. Research Design and Methods –We recruited 193 consecutive patients (aged 13–18 yr) with insulin-dependent diabetes mellitus during their regular quarterly visit to a diabetes clinic in a large urban hospital. Participants completed the Rosenberg Self-Esteem Scale, the Children's Depression Inventory, an assessment of the frequency of binging in the past 3 mo, and parallel forms of an adherence scale and a self-efficacy scale that were developed for use in this study. Results –Adolescents who reported lower adherence tended to report lower self-esteem (r = 0.45, P < 0.001) and self-efficacy (r = 0.57, P < 0.001), more depressive symptoms (r = −0.50, P < 0.001), more binging (r = −0.36, P < 0.001), and had higher HbA1c (r = −0.24, P < 0.001) than those with higher adherence scores. Together, the psychological variables accounted for 50% of the variance in adherence. There was no sex difference in reported binging, but, as expected, adolescent females reported less adherence overall (F[7,184] = 2.5, P = 0.018). Conclusions –Treatment adherence in adolescents with insulin-dependent diabetes mellitus is associated with behavioral and psychological variables. These findings suggest that specific behavioral and cognitive interventions could be used to improve adherence in those individuals who lack confidence in their ability to perform diabetes-related tasks.