Background: More than one-third of American adults are obese, and an elevated body mass index (BMI) is postulated to reduce the sensitivity of the clinical evaluation of the axilla. Clinical nodal examination is important in allocating breast cancer patients to appropriate axillary management. This study sought to determine whether BMI influences the rate of nodal positivity in women designated clinically as node-negative (cN0) by physical examination. Methods: Breast cancer patients deemed cN0 who underwent sentinel lymph node biopsy (SLNB) from February 2006 to December 2011 were identified from a prospectively maintained database. Clinicopathologic features including BMI and axillary surgery results were recorded and compared among pathologically node-negative and node-positive patients. Results: Overall, 5142 cN0 patients underwent 5262 SLNB procedures during the study period. Nearly one-third of the patients (28 %) were obese (BMI, >30 kg/m2). A positive SLN was identified in 25 % of the patients, and 84 % proceeded to axillary lymph node dissection. Predictors of SLN positivity included younger age, larger tumor size, high nuclear grade, multifocality, and lymphovascular invasion. An increased BMI did not correlate with a higher likelihood of SLN positivity (p = 0.6). The likelihood of cN0 patients having a high burden of axillary metastases (>3 positive nodes) was 4 % overall and, similarly, did not differ according to BMI (p = 0.4). Conclusion: Elevated BMI was not associated with a higher likelihood of SLN positivity or heavy nodal disease burden among women staged as cN0 by physical exam. These findings indicate that physical examination is appropriate and sufficient for preoperative axillary evaluation of women undergoing initial surgery regardless of patient BMI.