The goal of this research was to develop and evaluate measures of adolescent diabetes management self-efficacy and outcome expectations that reflect developmentally relevant, situation-specific challenges to current diabetes regimens. Self-efficacy for diabetes management, expected outcomes of adherence, adherence to the diabetes regimen, and glycemic control were assessed in 168 adolescents (ages 10-16 years) with type 1 diabetes. Factor analyses indicated a single scale for self-efficacy and two distinct factors representing positive and negative outcome expectations. Reliability and predictive validity of the new scales were supported. In regression analyses, self-efficacy and the interaction of self-efficacy with expectations of positive outcomes were significantly associated with diabetes self-management adherence and glycemic control in older adolescents. The effect of self-efficacy was greatest when adolescents had stronger beliefs in the beneficial outcomes of adherence. These brief measures can be used to identify youths at risk of poor diabetes self-management. Interventions targeting self-efficacy may lead to improved diabetes self-management.