ACOSOG Z0011 spares axillary dissection (AD) in breast conservation surgery (BCS) patients with T1/T2 tumors and 1-2 positive nodes. Current patterns of care and the impact of Z0011 on AD versus additional surgery rates for Medicare patients undergoing BCS are unknown. SEER data linked to Medicare claims for 1999-2005 were reviewed for women with invasive nonmetastatic breast cancer who underwent nodal staging on the same day as BCS. There were 3,280 women with T1/T2 tumors and positive nodes who underwent same-day nodal staging; 2,532 (77.2 %) of these women had 1-2 positive nodes. Assuming 25.7 % have extracapsular extension, 651 women would require AD. However, 1,881 women, or 57.4 % of those with T1/T2 tumors and positive nodes, would be spared AD. Meanwhile, among the 748 women having ≥ 3 positive nodes, 579 underwent same-day AD, but under Z0011, would now wait for permanent section. A total of 160 of these women underwent re-excision or completion mastectomy at a later date anyway, when delayed AD could be performed. The remaining 419 women with ≥ 3 positive nodes would require an additional surgery date for the sole purpose of completion AD. The Z0011 paradigm would consequently necessitate an additional surgery date for 1,070 (651 + 419) women, or 32.6 % of those with T1/T2 tumors and positive nodes. The Z0011 paradigm appears to increase the number of Medicare patients undergoing BCS who require an additional surgery date but decrease the number requiring AD to a greater extent. Future changes in the use of AD or axillary irradiation may yet modify that impact substantially.