Lymphatic mapping and sentinel lymph node (SLN) biopsy have changed the standard of surgical care for women with invasive breast cancer. The rate of successful axillary SLN identification varies from 90% to 99%. Recurrence rates after a negative SLN biopsy have been remarkably low. Internal mammary node drainage has been noted in 8% to 22% of cases, but whether to harvest these extra-axillary sites of drainage remains controversial. Because of the low morbidity associated with the lymphatic mapping procedure, all women with invasive breast cancer should be considered as candidates for this more accurate staging technique.