[영문]Objective: To examine the effects of health plan enrollment [health maintenance organizations (HMO) or fee-for-service (FFS)], a change in Medicare reimbursement policy which allowed for annual rather than biennial mammograms, and Health Plan Employer Data Information Set (HEDIS) measures on stage at diagnosis among older women with breast cancer.Methods: We used the population-based Surveillance Epidemiology and End Results (SEER)-Medicare database to identify all elderly women age 65-74 who were diagnosed with breast cancer from 1994 to 2002. We compared stage at diagnosis, demographic characteristics, and tumor characteristics for FFS or HMO enrollment in the periods before and after the 1998 policy change. We compared the effect of women age 65-69 whose mammography use in the HMO system is measured by HEDIS and those who are older (age 70-74).Results: We identified 20,106 women enrolled in FFS Medicare, and 10,751 women enrolled in an HMO. Women ages 65-74 who were enrolled in a Medicare HMO were more likely to be diagnosed at an early stage both before and after the policy change, but the disparity decreased from 4.7% to 2.3%, a relative change of 51.1%. The disparity was not specific to the ages included in the HEDIS measure.Conclusions: A decrease of 51.1% in the HMO-FFS disparity in breast cancer stage at diagnosis coincided with the 1998 change in Medicare mammography reimbursement policy. The existence of HEDIS measures for HMOs does not create a disparity in stage at diagnosis between those whose mammograms are measured by HEDIS (younger women) and those whose are not (older women).