Korean National Diabetes Program (KNDP) cohort study is a large-scale prospective multicenter investigation to discover the pathogenesis of type 2 diabetes in Korean patients. The study commenced in May 2006 and follow-up continued until March 2014 and included 4,265 participants. Among the participants, the crude prevalence of microvascular and macrovascular diseases of those checked for diabetes-related complications was determined, and the adjusted standard prevalence and standardization of the general population prevalence ratio (SPR) was estimated based on the 2005 Korean National Health and Nutrition Examination Survey (KNHANES) population demographics. Among the KNDP registrants, 43.2% had hypertension, 34.8% had dyslipidemia, 10.8% had macrovascular disease, and 16.7% had microvascular disease on initial evaluation. The SPR of the KNDP registrants was significantly higher than that of the KNHANES subjects after adjusting for demographics in the KNHANES population. For evaluate the annual incidence rate and risk factors for the progression of diabetic complication available data was analyzed. The annual nephropathic stage-to-stage transition rates in Korean patients with type 2 diabetes were higher than those noted in other ethnic groups. And the annual transition rates from no diabetic retinopathy to diabetic retinopathy were consistent with previous studies. For evaluate the clinical outcomes of KNDP cohort further verified using claims data from Health Insurances Review and Assessment Service of Korea. In evaluation of diabetic foot complication (DFC), the patients with DFC were significantly older than patients without DFC, and longer duration of hospitalization, and increased expenses. DFC were significantly associated with poor clinical outcomes and caused a substantial burden to the national healthcare system in Korea. Early diagnosis and appropriate management of Korean patients with type 2 diabetes is thus particularly important to prevent development of diabetic complications.