BACKGROUND: For clinical T1-2N0 breast cancer, sentinel lymph node biopsy (SLNB) has been shown in American College of Surgeons Oncology Group (ACOSOG) Z0011 to be sufficient for women with 1 to 2 positive sentinel lymph nodes with no added benefit for completion axillary lymph node dissection (ALND). Z0011 specified whole breast radiotherapy (RT) using standard tangential fields; however, later analysis showed variation in field design. We assessed nationwide practice patterns and examined factors associated with patients undergoing completion ALND and subsequent radiation field design. PATIENTS AND METHODS: Women with clinical T1-2N0 breast cancer who underwent breast-conserving surgery, axillary staging, and whole breast RT in 2012 to 2013 were identified in the National Cancer Database. Multivariable logistic regression modeling was used to examine axillary management and RT, adjusting for demographic and clinicopathologic factors. RESULTS: Among 83,555 patients meeting criteria, 9.3% underwent upfront ALND, 75.8% underwent SLNB only, and 14.9% underwent SLNB with completion ALND. From 2012 to 2013, upfront SLNB increased from 90.1% to 91.4% (odds ratio, 1.14; P < .001). Among 9474 patients that underwent SLNB with 1 to 2 positive sentinel nodes, 31.2% received completion ALND. Among patients with 1 to 2 positive sentinel nodes, SLNB increased from 65.8% to 72.1% from 2012 to 2013 (P < .001). For patients with 1 to 2 positive lymph nodes that underwent SLNB only, 63.4% underwent breast RT, whereas 36.6% received breast and nodal RT. CONCLUSIONS: Nationwide practice patterns of axillary management vary. Despite an increasing rate of SLNB, many patients still receive upfront and completion ALND. Furthermore, there is significant variation in RT field design, and modern treatment guidelines are warranted for this patient population.