Background: This paper reviews the implementation of the National Health Insurance (NHI/JKN) program regarding the Indonesian-Case Based Group (INA-CBG) payment system, including a response from hospital management, especially regarding INA-CBG rates and perceptions that low rates trigger "ineligible readmission" events, which are defined as "inpatient cases that returned for treatment in less than or equal to 30 days with either the same or a similar diagnosis." Objective: This paper aimed to show an ineligible readmission pattern (including number, type of hospital ownership, Casemix Main Groups (CMG), primary diagnosis, and differences in cost) in NHI/JKN implementation in the Sukabumi branch office. Methods: This study employed descriptive analytic research using the secondary data of hospitalization claims at 12 hospitals in Sukabumi City, Sukabumi Regency, and Cianjur Regency. Terms defined included inpatient readmission with the hospitalization status of early return or "recovered." Exclusions included "eligible readmission" diagnoses, such as beta thalassemia and chronic renal failure, and CMG. Results: Data were collected on 55,496 patients, which showed that the readmission rate was 18.76%, from which 45.64% had the same CMG with an exclusion, and 45.74% had both the same CMG and the same main diagnosis. The results showed that INA-CBG rates were higher than hospital rates. Conclusion: Ineligible readmissions are causing increased and unnecessary costs due to a lack of readmission regulation. Possible solutions could include the creation of a detection and warning application for potential fraud, INA-CBG rate improvements, and government support of improved health services in hospitals. © 2018 Journal of International Dental and Medical Research.