The National Health Insurance Database of Korea is an important resource for various clinical studies. Numerous nationwide observational studies have been performed with the database. The database has particular strength in 1) that complete nationwide information based on claims information can be assessed for tens of millions of individuals and 2) that general health examination results including laboratory measurements are stored. As the laboratory measurement includes serum creatinine and urinalysis results and end-stage kidney disease history is identifiable with the data, the database is also useful for nephrology studies. There have been studies 1) to know the epidemiology, 2) to assess the clinical significance of health exam variables 3) to evaluate a prognostic outcome, and 4) to investigate socioeconomics-related status in chronic kidney disease patients. The epidemiology of acute kidney replacement therapy, chronic kidney disease, and transplantation has been investigated with the database. The prognostic significance of metabolic abnormalities, including blood pressures, variabilities in body mass index in chronic kidney disease patients have been studied. Cardiovascular, psychiatry-neurology outcomes and infectious complications such as tuberculosis have been important clinical endpoints studied by the database. The nephrology studies utilizing the National Health Insurance database have power because large, nationwide events can be evaluated, thus has been acknowledged in the recent literature. Through this lecture, we will review the nephrology studies using the National Health Insurance database of Korea and share our experiences for the study topic which will be further extended in near future.