The sentinel node concept is valid for penile cancer, melanoma, breast cancer and is probably also applicable to other solid malignancies. Sentinel nodes are the one or two initial nodes in the regional nodal drainage basin encountered by the lymphatic effluent from a tumour, which can be identified with an injection of vital dye or other lymphogogue. Sentinel lymph node dissection (SLND), a minimally invasive procedure with negligible morbidity, has therefore been utilized as an alternative to complete axillary lymph node dissection (ALND) for staging breast cancer. Examination of sentinel nodes provides a focused histopathological assessment of tissue most likely to harbour metastases, providing enhanced staging accuracy with a low false-negative rate. Tumour-free sentinel nodes are predictive of a tumour-free axilla, thereby allowing for the possibility of SLND without ALND and sparing patients the morbidity of ALND. Most of the experience from SLND has been obtained for axillary sentinel nodes. However, sentinel nodes have been identified in nonaxillary sites, such as the internal mammary nodes, but data on SLND for these regions is scarce. The ultimate role of SLND in breast cancer, which may be to identify sentinel-node-negative patients or even those with sentinel node metastases who can safely avoid ALND without sacrificing regional control and possibly gain a therapeutic benefit, cannot be defined before we have the results of large trials that are currently in progress.