BACKGROUND: Glycemic index and glycemic load are used to facilitate glucose control among adults with type 2 diabetes, with a low glycemic index diet associated with improved glycemic control. OBJECTIVE: To examine long-term longitudinal associations between changes in glycemic index and glycemic load with glycemic and metabolic control among Latino adults with diabetes. DESIGN: Secondary data from intervention and comparison participants in the Latinos en Control trial (2006 to 2008) were analyzed. PARTICIPANTS/SETTING: Data on dietary intake and metabolic characteristics were from low-income, Latino adults (N = 238; 87.7% Puerto Rican) with type 2 diabetes. INTERVENTION: The Latinos en Control trial was a randomized clinical trial targeting diabetes self-management among Latinos with type 2 diabetes. Participants were randomized to a group-based behavioral intervention or usual care and followed through 12 months. MAIN OUTCOME MEASURES: Outcomes included hemoglobin A1c (HbA1c) levels, fasting blood glucose, lipid profiles, anthropometrics, and blood pressure. STATISTICAL ANALYSIS: Glycemic index and load were analyzed using data from three 24-hour dietary recalls conducted at baseline, 4 months, and 12 months. Repeated measures regression models were used to examine change in glycemic index and load associated with metabolic characteristics at 12 months. Covariates included sex, age, body mass index, blood pressure, total energy intake, medication use and intensity, physical activity, intervention status (intervention vs usual care), and time. RESULTS: Increases in glycemic index from baseline to 12 months were associated with increased logarithm of HbA1c levels (beta = 0.003; P = 0.034) and waist circumference (beta = 0.12; P = 0.026) over time, but not with fasting glucose, blood lipids, or body mass index. There was modest evidence to support small, positive associations between glycemic load and HbA1c levels and waist circumference. CONCLUSIONS: Lowering glycemic index is associated with improvements in certain metabolic risk factors among Latinos with diabetes. Targeting glycemic index may be an important component of dietary strategies for diabetes self-management. All rights reserved.