Although adherence has been identified in practice guidelines for youth with type 1 diabetes to promote optimal glycemic control, there has been no systematic integration of studies investigating the adherence-glycemic control link. This recommendation partly stemmed from the Diabetes Control and Complications Trial (DCCT); however, this trial did not comprehensively measure adherence and had only 195 adolescents. Our goal was to determine the magnitude of the adherence-glycemic control link in pediatric type 1 diabetes and evaluate its correlates. Our data sources were PubMed (1950-2008), Scopus (1950-2008), and references from reviews in pediatric type 1 diabetes. Studies that included youth under age 19 with type 1 diabetes and a reported association between adherence and glycemic control were eligible for inclusion. Articles were not included if they contained youth with type 2 diabetes, had study samples that overlapped with other studies, or the results came from intervention studies. Of the eligible 26 studies, 21 had sufficient statistical data. Two authors independently extracted information by using a standardized protocol. Agreement between coders was high. The mean effect size across 21 studies, including 2492 youth with type 1 diabetes, was -0.28 (95% confidence interval: -0.32 to -0.24). As adherence increases, A1c values decrease. No sample or disease characteristics were correlates of the adherence-glycemic control link. Pre-DCCT studies had a mean effect size of -0.32 (8 studies; 1169 participants) compared with -0.25 in post-DCCT studies (13 studies; 1323 participants). This meta-analysis supports the adherence-glycemic control link in pediatric type 1 diabetes. The weaker post-DCCT association suggests that the approach to intensive diabetes management has shortcomings. We conclude that this is because of a mismatch between what scientists and clinicians know is the best way to manage pediatric type 1 diabetes and the capabilities of youth and their families.