The sentinel node (SN) concept was clearly outlined by Virchow in the mid-nineteenth century, and Braithwaite used the term "glands sentinel" in 1923. However, it was not until Morton, Cochran et al. published their landmark report in 1992 that the clinical relevance of the SN was fully appreciated. Since then, the validity of the concept has been confirmed in studies undertaken at a number of centers worldwide. It has become clear that SN status accurately reflects the status of the entire regional node field, not only in patients with melanoma but also in those with breast cancer and a wide range of other primary malignancies. New insights into lymphatic anatomy have been gained by preoperative lymphoscintigraphy, and the original blue dye mapping technique for SN identification has been supplemented by intraoperative use of a hand-held gamma probe to identify radioactivity in colloid particles injected at the primary tumor site. It has become clear that all three methods are required to achieve optimal accuracy of SN identification. Although SN assessment provides very important prognostic information, the results of randomized trials must be awaited to determine whether selective sentinel lymphadenectomy, with full regional node dissection if a positive SN is found, is of any therapeutic value. It is possible that SN positivity is merely a marker of disease that has the potential for hematogenous dissemination and systemic metastasis. As follow-up times extend, reported false-negative SN rates are increasing, and ways to reduce these false-negative rates are therefore being actively sought. Attempts are being made to increase the accuracy of SN identification, and to confirm true SN identity both at the time of surgery and retrospectively. The ultimate objective is to develop minimally invasive and even non-invasive methods of SN assessment, Proton magnetic resonance spectroscopy is one technique that might make it possible to achieve this goal, and avoid the present morbidity and cost of operative SN removal.