This goal of this research was to evaluate the cost-effectiveness of the National Cancer ScreeningProgram (NCSP) for breast cancer in the Republic of Korea from a government expenditure perspective. In2002-2003 (baseline), a total of 8,724,860 women aged 40 years or over were invited to attend breast cancerscreening by the NCSP. Those who attended were identified using the NCSP database, and women weredivided into two groups, women who attended screening at baseline (screened group) and those who did not(non-screened group). Breast cancer diagnosis in both groups at baseline, and during 5-year follow-up wasidentified using the Korean Central Cancer Registry. The effectiveness of the NCSP for breast cancer wasestimated by comparing 5-year survival and life years saved (LYS) between the screened and the unscreenedgroups, measured using mortality data from the Korean National Health Insurance Corporation and theNational Health Statistical Office. Direct screening costs, indirect screening costs, and productivity costs wereconsidered in different combinations in the model. When all three of these costs were considered together,the incremental cost to save one life year of a breast cancer patient was 42,305,000 Korean Won (KW)(1 USD=1,088 KW) for the screened group compared to the non-screened group. In sensitivity analyses,reducing the false-positive rate of the screening program by half was the most cost-effective (incrementalcost-effectiveness ratio, ICER=30,110,852 KW/LYS) strategy. When the upper age limit for screening wasset at 70 years, it became more cost-effective (ICER=39,641,823 KW/LYS) than when no upper age limitwas set. The NCSP for breast cancer in Korea seems to be accepted as cost-effective as ICER estimates werearound the Gross Domestic Product. However, cost-effectiveness could be further improved by increasingthe sensitivity of breast cancer screening and by setting appropriate age limits.