Little is known about how behavioral health (BH) conditions affect health care costs of patients with cancer in Japan. The purpose of this study is to evaluate the magnitude of general medical claims expenditures for individuals with cancer who use or do not use BH services in Japan. The study used a health insurance claims database for more than 3 million enrollees in Japan. All health plan enrollees (18 y or older) who had tumors without metastasis or metastatic solid tumors defined by the Charlson Comorbidity Index were included in the study (n= 20,260). Measurements included total claims expenditures for BH and medical services. The proportion of enrollees using BH services was 12.8%. BH service users accounted for 17.7% of total health service spending. Mean annual cost of total health care services were 1.5 times higher in BH users than those with no BH use, whereas the median was 1.8 times higher. Mean annual medical cost alone for BH users was 1.3 times higher than that for non-BH users, whereas the median was 1.5 times higher. The findings suggest the importance for the Japanese medical system to address BH needs of patients with cancer and introduce fiscal efficiencies to cancer care. Strategic implementation of effective integrated care services for patients with cancer should be considered in Japan.