Background: To investigate the current status of long-term care services for patients with dementia and lifetime medical costs for dementia in South Korea. Methods: This study utilized the National Health Insurance Service-National Health Information Database (NHIS-NHID) from January 2013 to December 2017. The prevalence and incidence of dementia was estimated by extracting people who were diagnosed and treated with dementia (age≥45 years) from the database. The use of long-term care services by the elderly with newly diagnosed dementia was also investigated. Additionally, the lifetime medical expenses for dementia were estimated using data on a single year’s medical costs, population data, and a life table from Statistics Korea. Results: The prevalence of dementia increased from 2015 to 2017, while the incidence of dementia gradually decreased. Among the patients with newly diagnosed dementia, approximately 30% used the long-term care services, while 4th graders accounted for the highest proportion every year. The older the individual and the lower their income quartile, the shorter the time they took to apply for long-term care services after diagnosis of dementia. The total medical expenses per capita increased steadily every year, and the lifetime medical expenses were higher for women than men. Half of the lifetime medical costs of dementia occurred after 67 years of age for men and 83 years for women. Conclusion: This study suggests that medical, social, and political measures are needed to effectively manage the long-term care of service recipients and prepare for rising medical costs for dementia.