Equity in health care services has been prioritized on the Korean government's policy agenda since the government-driven national health insurance achieved universal coverage in 1989 along with the final inclusion of the self-employed as beneficiaries. The purpose of this study is to identify disparities in the utilization of health care services, especially cancer inpatient services among different income groups in Jeju Island of South Korea. We analyzed the national health insurance data about qualification of beneficiaries and utilization of health care services consumed by Jeju Island's residents for 1 year of period (from January to December 2000) and acquired their utilization features of cancer inpatient services. The independent variable was 10 different income levels according to the national health insurance fee imposed on each household in 2000. The dependent variable was the volume of cancer inpatient services utilized, that was measured by admission days and costs for treatment. The utilization of cancer inpatient services in the 10 different income groups was analyzed in three geographical categories of medical institutions: (1) within Jeju Island; (2) outside Jeju Island; (3) South Korea in total. We calculated the concentration-indices of cancer inpatient services utilization in admission days and cost as a pair amongst these three geographical categories each. Both of the concentration-indices were negative for the category of 'within Jeju Island', positive for that of 'outside Jeju Island', and positive for that of 'South Korea in total'. These results suggest the relatively poor experience considerable inequality in the utilization of cancer inpatient services in Jeju Island, because lower income groups have higher incidence rates in most cancers and inevitably have more needs in health services.