International Classification of Disease (ICD-10) is widely used as a crucial reference not only in the medical diagnosis of diseases but also within the health insurance system. It makes possible for medical personnel to make decisions systematically and for the people working in the health insurance or public health industries to better understand medical issues. However, this classification is often not enough or acceptable in a clinical setting. Many countries amend in their own way to make it more appropriate for their people. Korean Classification of Disease (KCD-5) was made by adding a 5 digit code for some diseases to clarify the conditions of the patients. The authors found problems of KCD-5 in temporomandibular disorders and several related medical problems. Medical treatment for these problems had not been covered even by public health insurance until 2000 in Korea. For the last decade, private insurance companies have introduced new items for reimbursement of the treatment fees the patients actually pay. The authors assumed that many patients with these medical problems encountered difficulties in the reimbursement from private insurance companies because KCD-5 did not classify these medical conditions appropriately. An overview of KCD-5 and suggestions for improvement are introduced in this study.