OBJECTIVES: To investigate the influence of the portion of medical expense (30% of total amount of medical cost) paid individually on physicians' attitude toward treatment for the patients with breast cancer in Japan. METHODS: A total of 165 physicians from board members of Japanese breast cancer society (363 physicians) completed self-report questionnaires. RESULTS: One hundred and forty-two out of 165 physicians (87.7%) were surgeons, which reflected peculiar circumstance; surgeons usually are involved in surgical treatment as well as chemotherapy in Japan. Seventy-seven physicians (48%) had an experience of having been asked by the patient for cheaper treatment because of excessive individual payment. One hundred and twenty physicians (74%) tried to select the treatment, giving greater importance on the cost individually paid by the patients. The difference between actual cost and the cost roughly estimated by the physicians was the greatest in the treatment using molecular targeting drugs (i.e. trastuzumab) and was smaller in hormone therapy as well as conventional chemotherapy. The rate of physicians unfamiliar with following national medical/welfare system in Japan was “refunding from social assuror” (12%, “interest free-loan by local government (46%) and “tax reduction for medical expenses” (21%). The physicians supporting expansion of the portion of the medical expense uncovered by social insurance was three times greater than those negative for it. CONCLUSION: 1) About 60 percent of breast cancer specialists had keen senses on an economical side of the treatment especially on the portion of medical expense paid individually. 2) Excessive individual payment exerted an influence on continuing effective chemotherapy.