OBJECTIVES: To evaluate the magnitude of general medical claims expenditures (ie, medical service use) for individuals who use and do not use behavioral health (BH) services in the Japanese free-access medical insurance system to determine if BH patients use substantially more health services, as has consistently been reported in the United States. STUDY DESIGN: Retrospective comparison of Japanese occupation-based total health services use for enrollees with and without comorbid BH conditions. METHODS: The study used a health insurance claims database for more than 3 million enrollees in Japan. All health plan enrollees (18 years and older) who had at least 1 diagnosis of a chronic medical condition were included in the study (N = 192,613). Measurements were total claims expenditures for BH and medical services. RESULTS: The proportion of enrollees using BH services was 14.3%. BH service users accounted for 21.1% of total health service spending. Annual total costs of BH service users were 1.6 times higher than those of non-BH users. Annual medical costs of BH users were 1.3 times higher than those of non-BH users. CONCLUSIONS: The results of this Japanese cohort study show that patients with concurrent BH conditions and chronic medical illnesses have substantially lower total health care costs than numerous studies have demonstrated in US populations. This is perhaps in part due to the integration of medical and BH claims payment and care delivery in Japan, an approach that the US health system may wish to consider testing.