When melanoma spreads, it invariably does so by the lymphatic system. The first lymph node to be affected is called the sentinel node, and this node can be identified by injecting dye and a radioactive tracer at the primary tumour site. During sentinel lymph node biopsy, the sentinel node is located by a hand held γ probe and confirmed as the sentinel node using blue dye staining; it is then removed for histology. About 80% of patients have no melanoma in the sentinel node. In the remaining patients, the tumour burden varies from tiny deposits of melanoma in the subcapsular sinus to complete replacement of several sentinel nodes with extracapsular spread. Patients who are sentinel node negative have a better prognosis than those who are sentinel node positive, and the prognosis worsens as the tumour burden increases. But evidence is accumulating that some tiny deposits of melanoma in the sentinel node have no prognostic relevance and will not progress or disseminate further as determined by the patient’s immune system and other host factors. Attributing a poorer prognosis to the presence of these tiny deposits in the sentinel node is called prognostic false positivity. This can lead to patients being mistakenly upstaged, given inaccurate prognostic information, undergoing …