In Japan, medical expenses are increasing, which has been shifting from 36.6 trillion yen in FY 2010 to 40.0 trillion yen in FY 2010. 1 The system changed to the conventional payment method, and a comprehensive medical expenses payment system (DPC) centered on patients (diseases) was introduced. Medical expenses according to this method are calculated from the main disease name diagnosed at the time of admission. Therefore, it depends on the accuracy of the diagnosis name. Regarding the relevance of this diagnosis, there is one lesson from the trend of the death cause statistic of our country. In this study, we aimed to estimate the effect on medical expenses when the diagnosis name change similar to the death causes statistics around 1995 occurred, using DPC data. The targeted DPC data relates to discharged patients from April 2013 to March, 2013 DPC Hospital Group I 80 DPC Hospital II Group 90 DPC Hospital III Group 1327 Hospital. Diagnosis group for each diagnosis group classification for each diagnosis group classification. Based on the average number of days of hospitalization for classification names, in-hospital medical points were calculated, multiplied by the number of cases and multiplied by 10 to make medical cost corresponding to the relevant diagnosis group classification name. Next, heart disease, cerebrovascular disease, and malignant tumor were defined for each diagnosis, and the number of medical cases, the medical expenses per capita, the total medical cost, and the average number of hospital days were calculated for each diagnosis. We estimated the change in medical expenses assuming that 20% of cases of heart disease were moved to cerebrovascular disease and malignant tumor by 10% each. This change in DPC medical expenses was estimated as the change in medical expenses by multiplying the total of DPC medical expenses by the ratio of medical expenses of 39.3 trillion yen in fiscal year 20 of medical expenses in Japan in fiscal year 2013. The sum total of DPC medical expenses for Heisei 20 years was 2.03 trillion yen. The DPC medical expenses were 2.21 billion yen lower after the movement than before the diagnosis was moved. Based on the above, it is estimated that medical expenses in Japan will decrease by 40.9 billion yen when the diagnosis of heart disease moves to cerebrovascular disease and malignant tumor by 10% each. It is necessary to examine the possibility of suppression of medical expenses in more detail by expensive treatment and aggregation by age group.