Sentinel lymph node mapping is used as a diagnostic method in order to increase staging accuracy without the well-known morbidities of radical lymphadenectomy. The sentinel node is defined as the first node to receive lymphatic drainage from a primary tumor. The sentinel node concept postulates that if the first draining node is negative for metastasis, the remaining lymph nodes in the nodal basin can be spared. Thus one can predict the status of the nodal basin with high accuracy. It also shows that lymphatic spread seems to follow certain rules that do not concern the whole lymphatic basin. Skip metastases were proven to be rare in breast and gastric cancer. The main issue in sentinel lymph node mapping remains the improvement of staging accuracy for detection of lymph nodes most likely to develop metastasis as well as reducing morbidity by planning lymphadenectomies individually for each tumor and each patient.