As the current classifications of causes of death and disease used in Japan's official statistics are constructed in accordance with ICD-10, these classifications would be necessary to be updated in accordance with the introduction of the new classification of disease, namely ICD-11. Purpose of this study is to develop a new classification of the “the disease classification for Japan” based on the ICD-11, and to analyse the changes of the patient survey between current and new classifications. We develop a new “the disease classification for Japan” based on the ICD-11 using the ICD-10/11 mapping table developed by WHO and patient survey of Japan. We estimated the changes in the aggregated number of diseases 2021 by the current and newly developed classification. As the new classification was developed based on the structure of ICD-11, the number of patients aggregated number of diseases was estimated differently between current and new classifications. This study indicated that the introduction of ICD-11 would be influenced on the Japan’s official statistics. It is necessary to conduct a further study on the impact of the ICD-11 introduction on the Japan’s official statistics.