The current national health-insurance system of the Republic of Korea uses the negative-list method to determine benefit coverage, which includes most medical services. However, financial limitations have led to frequent conflicts between medical-service providers and the Health Insurance Review and Assessment Service (HIRA) about the inclusion of specific service-providers' practices within benefit coverage. The role of HIRA is to determine whether payments claimed by service providers are clinically valid and formulated in a cost-efficient manner. This article describes the present state and structure of the benefit system in the Korean national health-insurance system. We focus on issues of arbitrary uninsured benefits that may arise when service providers request patients to pay in full (with their approval) for a service that is not included in the benefits, according to the National Health Insurance Act. We also consider the legal treatment of arbitrary uninsured benefits in Korea and other countries. We suggest measures to improve the payment system for arbitrary uninsured benefits in Korea. Laws and regulations should be revised to cover these arbitrary uninsured benefits in a manner that can be agreed upon by HIRA, service providers, and patients.