This year marks the 40th anniversary of the introduction of National Health Insurance (NHI) which has contributed to improving public health and accessibility. This article aims to show the trends of main indicators during the last 40 years. NHI has achieved rapid expansion of target population (1977–1989). The percentage of population covered increased from 8.8% in 1977 to 94% in 1990. The average number of visit days per person was 0.75 in 1977 but significantly increased to 31.11 in 2015. In 2015, NHI revenues were 52.4 trillion won and expenditures were 48.2 trillion won which is 9.5 times and 9.6 times higher than in 1995. NHI achieved universal coverage in short period of time and has contributed to improving the healthcare status. However, there still remain problems including low-benefit coverage and high out of pocket money. Therefore, the effort to reform these problems is needed.