The objective of this study was to investigate the relationship between prior screening mammography use and cancer stagetumor size at diagnosis for women aged 67 and older diagnosed with primary breast cancer in 1994, 1995 or 1996 and having a linked SEER- Medicare record. of interest was the effectiveness of screening mammography in women aged 75 and older compared to women aged 67-74, and the effectiveness of screening mammography in non-Hispanic whites compared to African Americans and Hispanics. Women 75 and older were significantly more likely to be diagnosed with non-local disease stage IIA or higher and have larger tumors than women 67 to 74 years of age. However among regular users of mammography, both women 65-74 years old and 75 years and older were diagnosed with the same size tumor and same percent non-local stage tumors. These results were similar after adjusting for sociodemographic and comorbidity information. African American and Hispanic women were significantly more likely to be diagnosed with non-local stage disease and larger tumors than white women. However when women were regular users of mammography the difference was not significant. Regular use of screening mammography eliminates differences in tumor size and stage of cancer at diagnosis observed in older women and minority groups.