OBJECTIVE This study examined the long-term effectiveness of the national diabetes quality assessment program (NDQAP) in diabetes. RESEARCH DESIGN AND METHODS From the Health Insurance Review and Assessment Service database, 399,984 individuals with diabetes who visited a primary care clinic from 1 July 2012 to 30 June 2013 were included and followed up until 31 May 2021. The NDQAP included five quality assessment indicators: regular outpatient visits, continuity of prescriptions, regular testing of glycated hemoglobin and lipids, and regular fundus examination. Cox proportional hazards models estimated hazard ratios (HRs) and 95% confidence intervals (CIs) for diabetes complications and all-cause mortality by the achievement of quality assessment indicators. RESULTS During the mean follow-up duration of 7.6 ± 1.8 years, 20,054 cases (5.0%) of proliferative diabetic retinopathy (PDR), 6,281 end-stage kidney diseases (ESKD; 1.6%), 1,943 amputations (0.5%), 9,706 myocardial infarctions (MIs; 2.4%), 26,975 strokes (6.7%), and 35,799 all-cause mortality (8.9%) occurred. Each achievement of quality assessment indicator was associated with a decreased risk of diabetes complications and allcause mortality. Individuals who were managed in high-quality institutions had a lower risk of PDR (HR 0.82; 95% CI 0.80–0.85), ESKD (HR 0.77; 95% CI 0.73–0.81), amputation (HR 0.75; 95% CI 0.69–0.83), MI (HR 0.85; 95% CI 0.82–0.89), stroke (HR 0.86; 95% CI 0.84–0.88), and all-cause mortality (HR 0.96; 95% CI 0.94–0.98) than those who were not managed in high-quality institutions. CONCLUSIONS In Korea, the achievement of NDQAP indicators was associated with a decreased risk of diabetes complications and all-cause mortality.