Sentinel lymph node biopsy (SLNB) has replaced the routine level I and II axillary lymph node dissection (ALND) for women with clinically node-negative T1 and T2 breast cancer. Studies have shown that SLNB is highly predictive of axillary nodal status with a false-negative of rate less than 10%. Our purpose was to address some of the ongoing controversies about this procedure, including technical issues, use of preoperative lymphoscintigraphy, internal mammary lymph node biopsy, criteria for patient selection (in intraductal carcinoma?), its staging accuracy, and the clinical approach when a SLNB was found to be negative or positive on pathologic examination. After the revision of the American Joint Committee on Cancer (AJCC) staging system for breast cancer in 2002, the evaluation of internal mammary lymph nodes and determination of micrometastases by hematoxylin-eosin or by immunohistochemistry have become increasingly important in staging of patients. Recent guideline recommendations developed by the American Society of Clinical Oncology (ASCO) Expert Panel in 2005 are also discussed. Long-term follow-up results of ongoing studies will provide more accurate assessment of the prognostic significance of SLNB and its value in the prevention of breast cancer-related morbidity in axillary staging compared to ALND.