After clinical staging, the single most important prognostic factor for patients with newly diagnosed primary breast cancer is the presence or absence of detectable metastases to axillary lymph nodes when examined by conventional light microscopy. More sensitive methods of determination of lymph node status, such as evaluation of serial sections, immunohistochemical staining, and use of molecular biological assays increase the rate of detection of micrometastases. Although the feasibility of enhanced detection of occult axillary metastatic disease is well established, the prognostic significance of such detection is only recently starting to emerge. Furthermore, the enormous recent interest in the application of sentinel lymph node biopsy as an alternative to the evaluation of the entire axilla in patients with breast cancer makes the first-time detailed evaluation for micrometastases practically feasible. In this review the different methods of detecting micrometastatic disease in the axilla and the significance of such findings are discussed.