A modern technique, mostly developed thanks to progress in radioisotopic technology, only recently has it become part of standard clinical practice. Following injection of a lymphotropic radioactive tracer – the same as the one used in lymphoscintigraphy – coupled with a portable gamma-camera, preferential lymphatic drainage pathways are detected, with a good level of accuracy, as well as reference lymph nodes for a specific body region, generally close to the site of a malignant tumor (the “sentinel” lymph node is the first drainage lymph node). The goal is to support the surgeon in performing a surgical lymphadenectomy by targeting lymphatic-lymph node structures at a higher risk of tumor invasion, while limiting surgical invasiveness, and, indirectly, reducing its complications.