INTRODUCTION: Sentinel lymph node is defined as the first lymph node on the direct drainage path from the primary tumor. The sentinel lymph node biopsy (SLNB) procedure in melanomas is based on the premise that if the sentinel lymph node is negative for metastatic tumor, then there is a very high likelihood that the remainder of the regional lymph nodes are also free of tumor. SLNB is a reliable staging procedure and a powerful prognostic indicator. INDICATIONS: SLNB is recommended for all melanomas 1 mm or greater in thickness. SLNB is also useful in following situations: ulcerated melanoma, tumors with more than 50% regression, tumors in vertical growth phase, positive deep margin in biopsy specimens, tumors less than 1 mm thick but with Clark Level IV, and tumors with high mitotic activity. PROCEDURE: A blue dye (Lymphazurin blue) and/or a radioisotope tracer (99Tc-sulfur colloid) are injected in the vicinity of the primary tumor (as shown here). They ultimately end up in the sentinel lymph node via lymphatic drainage. The sentinel lymph node is identified by visual inspection as well as by measuring highest radioactivity (dynamic lymphoscintigraphy). The removed lymph node is sent to pathology where it is bivalved or serially sectioned and processed for routine histology. For additional details on sentinel lymph node biopsy, Click here. Image courtesy of: Eddy Hsueh, MD, Professor of Surgery, Saint Louis University, St. Louis, Missouri, USA. Used with permission.