This study sets out to examine the relationship between both surgeon and hospital volume and five-year survival rates for breast cancer patients. We performed Cox proportional hazard regressions on a pooled population-based database linking the Taiwan National Health Insurance Research Database with the 'cause of death' data file, covering the three-year period from January 1997 to December 1999. Of the 13,360 breast cancer resection patients in our study sample, the five-year survival rates, by surgeon volume, were 77.3% in the high-volume group (>201 cases), 76.9% in the medium-volume group (45-200), and 69.5% in the low-volume group (<or=44). The five-year survival rates, by hospital volume, were 77.3% for high-volume hospitals (>585 cases), 74.5% for medium-volume hospitals (259-585) and 72.1% for low-volume hospitals (<or=258). Cox regression analyses show that the risk of death for patients treated by low-volume surgeons was up to 1.305 times (P < 0.001) as high as the risk for those treated by high-volume surgeons. Similarly, the risk of death for patients whose resections had been performed in low-volume hospitals was 1.484 times (P < 0.001) as high as the risk for those whose resections had been performed in high-volume hospitals. High surgeon or hospital volume contributes significantly to patient outcomes and may be regarded as an overall indicator of high treatment quality; we therefore strongly recommend that the healthcare authorities reveal to the public all of the relevant information on provider performance and caseloads in order to assist them to make the optimum choice when surgery becomes necessary.