The aim of this study was to examine the relationship of youth's involvement in diabetes-related decisions to adherence. Children and adolescents (8-19 years) and their parents (N = 89) completed the Decision Making Involvement Scale and the Self Care Inventory, a self-report measure of adherence. After controlling for youth age, the degree to which youth expressed an opinion and information to parents was associated with better parent- and youth-reported adherence. The degree to which parents expressed an opinion and information to youth was associated with worse parent-reported adherence. Joint decision-making behaviors (e.g., negotiation; provision of options) also were associated with better youth-reported adherence. Encouraging youth to express opinions and share illness-related information with parents during illness management discussions may improve adherence. Additional research is needed to identify mechanisms of effect and determine associations between decision making involvement and health behaviors and outcomes over time.