Despite the widespread use of sentinel lymph node biopsy (SLNBx) in the surgical management of breast cancer patients, several areas remain controversial. The following controversies are reviewed: Learning curves and validation studies. There clearly is a learning curve, and a completion ALND should be done until adequate proficiency is exhibited, both in terms of identification and false-negative rates. Location of injection. Intradermal injection offers superior identification rates compared with peritumoral injection, with comparable false-negative rates. Subareolar injection is as accurate as peritumoral injection. The value of scintigraphy. Routine scintigraphy does not enhance identification or false-negative rates. Mapping agents. Blue dye and radioactive tracer combined to provide a higher identification rate than either used alone.SLNBx in DCIS. In patients with a high risk of microinvasion, such as large tumors, a mass or high-grade DCIS-SLNBx is justified.SLNBx following neoadjuvant chemotherapy. Although there is evidence that SLNBx after neoadjuvant chemotherapy may be accurate, these data should be applied cautiously. Implications of non axillary SLN, especially internal mammary nodes. Data do not support routine resection of internal mammary sentinel lymph nodes outside a clinical trial. Implications of micrometastases in the sentinel lymph node seen only on immunohistochemistry. Since the significance of such metastases is unclear, decisions regarding treatment of these patients should be individualized. The value of completion axillary lymph node dissection. Is being addressed in clinical trials. Until those studies mature, completion ALND should be performed for patients with SLN metastases, but may be abandoned for patients with a negative SLN.