Objective: With the accelerated population aging, multimorbidity has become an important healthcare issue. However, few studies have examined multimorbidity and its impact on the use of medical and long-term care services in Japan. Therefore, this study aimed to examine the association between multimorbidity and the use of medical and long-term care services among older adults living in the depopulated mountainous areas of Japan.Patients and Methods: A cross-sectional study was conducted using insurance claims data from late-stage medical insurance and long-term care insurance (April 2017 to March 2018) for older adults ≥75 years residing in a mountainous area in the Tottori prefecture. In addition to the descriptive analysis, multiple generalized linear regressions with family gamma and log-link functions were used to examine the association between the number of morbidities and total annual medical and long-term care expenditures.Results: A total of 970 participants ≥75 years were included in the analysis. Participants who had two or more morbidities constituted 86.5% of the total sample. Furthermore, participants with mental disorders were found to have more comorbidities. The number of comorbidities is associated with higher medical and long-term care expenditures.Conclusion: Multimorbidity was dominant among late-stage older adults living in depopulated mountainous areas of Japan, and the number of morbidities was associated with higher economic costs of medical and long-term care services. Mitigating the impact of multimorbidity among older adults in depopulated regions of Japan is an urgent challenge. Future research should investigate the degree and effectiveness of social protections for vulnerable older adults living in remote areas.