OBJECTIVE: To describe results of cervical cytology screening among low-income and uninsured women in the National Breast and Cervical Cancer Early Detection Program. METHODS: We analyzed data from 750,591 women who received their first Papanicoiaou (Pap) test in the program between July 1995 and March 2001. RESULTS: Nearly 85%of the women were aged 40 years or older. Almost half were members of racial or ethnic minority groups. Overall, the percentage of abnormal Pap test results decreased with increasing age. The rates of cervical intraepithelial neoplasia (CIN) were highest in the younger age groups but the rate of invasive cancer increased with age. White women had the highest age-adjusted percentage of abnormal Pap test results and the highest rate of biopsy-confirmed CIN 2 or worse. CONCLUSIONS: In this nationwide screening program, only 7%of all biopsy-confirmed high-grade cervical lesions (CIN 2 or worse) were invasive cancer. This underscores the success of Pap screening in identifying preinvasive disease and preventing cancer. OBJECTIVE: To describe results of cervical cytology screening among low-income and uninsured women in the National Breast and Cervical Cancer Early Detection Program. METHODS: We analyzed data from 750,591 women who received their first Papanicoiaou (Pap) test in the program between July 1995 Overall, the percentage of abnormal Pap test results decreased with increasing age. The rates of cervical intraepithelial neoplasia (CIN) were highest in the younger age groups but the rate of invasive cancer increased with age. White women had the highest age-adjusted percentage of abnormal Pap test results and the highest rate of biopsy-confirmed CIN 2 or worse. CONCLUSIONS: In this nationwide screening program, only 7% of all biopsy-confirmed high-grade cervical lesions (CIN 2 or worse) were invasive cancer. This underscores the success of Pap screening in id entifying preinvasive disease and preventing cancer.