Joslin Diabetes Center's Registry and Risk Stratification System collects data on key measures of diabetes care and provides diabetes decision support to primary care providers. Specifically, this system identifies high-risk patients in a population, recommends patient-specific interventions based on Joslin's clinical guidelines, and reports a clinic's process and quality metrics for benchmarking and regional comparisons. This article describes Joslin's system and its impact on the quality of diabetes care in the primary care setting.