We performed a study to assess whether higher quality performance by Medicare managed care plans was associated with withdrawal. METHODS: Taking each county where a contract was active as a unit of analysis, this was a cohort study of Medicare managed care plans active in 2310 contract-county combinations in 1997 and followed for three years. We measured quality using fourteen indicators from the Health Employer Data and Information Set which we collapsed into four summary measures. We used a separate Cox proportional hazards regression for each indicator and each summary measure to assess the association of high quality care with time-to-withdrawal from Medicare while adjusting for market, organizational, environmental, and demographic factors. RESULTS: Of 2310 managed care contract-county combinations, 877 (38%) withdrew. The withdrawal rate among plans with high scores on a summary clinical quality measure was onefifth that for low scorers (4.2% v. 20.5%). For the summary ambulatory care access measure, the corresponding ratio was two-fifths (12.8% v. 32.0%). Lower payment rates were associated with higher withdrawal risk, contrary to plan claims, with higher clinical and ambulatory care access quality performance. In separate multivariable analyses, both high summary clinical performance (HR 0.18, 95%CI 0.08 ± 0.42), and high summary ambulatory care access performance (HR 0.53, 95%CI 0.27 ± 1.07) were independently associated with lower withdrawal risk. There was no independent association between either physician qualification or primary care provider stability measures and withdrawal. CONCLUSION: Managed care plans that continue to provide care to Medicare beneficiaries have higher average performance on clinical and ambulatory care access measures than plans that withdrew. System (BI-RADS) category 4 assessments (suspicious for malignancy) or category 5 assessments (highly suggestive of malignancy) were considered positive and in need of biopsy. These mammograms were matched to a subsequent biopsy obtained by fine needle aspirate, core biopsy, or surgery. We calculated the proportion of patients who had biopsies performed within 30 days, had biopsies within 1 to 12 months, and not biopsied within 12 months after the positive mammogram. RESULTS: 5,713 mammograms met eligibility criteria. 57.8% of mammograms were followed by biopsy within 1 month, 18.5% within 1 month to 12 months, and 23.8% did not have a biopsy within one year. There was a significant variation (p < .001) in time to biopsy by facility with a range of 33.5% to 77.5% of patients biopsied within one month and 9.3% to 60.0 % not having had a biopsy within one year. CONCLUSION: Though a majority of women received an expedient biopsy after a positive mammogram, the large proportion of women having a delayed biopsy or apparent lack of biopsy is of concern.