The importance of comprehensive geriatric assessment (CGA) is increasing in aging societies worldwide. However, there are few comprehensive studies on CGA, resulting in a limited understanding of its implementation rate, temporal changes and factors associated with its implementation. We aimed to investigate the implementation status of CGA and its regional variance in Japan. Using the Diagnosis Procedure Combination database, we investigated CGA trends, and identified the patient, hospital and regional factors associated with its implementation. We identified patients aged ≥65 years who were admitted for the first time between 2016 and 2020 with a diagnosis of stroke, heart failure, pneumonia, bone fracture or colorectal cancer. We examined the CGA implementation rate according to patient and hospital characteristics. We also investigated temporal changes and tendencies to carry out CGA in different prefectures. A total of 1 974 817 patients were analyzed, of whom 570 696 (28.9%) underwent CGA. The implementation trend increased steadily from 25.3% in fiscal year 2016 to 33.4% in fiscal year 2019. The implementation rate also increased with patient age (30.3% in patients aged ≥95 years). Regional variations in its implementation status were observed, with a higher tendency to be implemented in areas near major metropolitan regions. A trend toward carrying out CGA for colorectal cancer, but not for other diseases, has been observed in eastern Japan. Although CGA is increasingly carried out, considerable regional differences remain in its implementation status. Initiatives to reduce variations are necessary. Geriatr Gerontol Int 2024; ••: ••-••.