There is no consensus on the definition of a hot, nonblue sentinel lymph node (SLN), despite the widespread use of radiocolloid in SLN mapping.A retrospective review of 592 patients with malignant melanoma who underwent SLN mapping was performed. Ex vivo SLN counts and nodal bed counts were obtained by using a gamma probe. The size of each metastatic deposit in an SLN was defined as macrometastases (>2 mm), micrometastases (2 mm, 270 +/- 792 [NS]; < or =2 mm, 446 +/- 693 [NS]; isolated melanoma cells/cluster of cells, 677 +/- 1189 [P =.036]). Overall, 16 (1.4%) of the SLNs collected had an overall ratio of < or =2. This included two positive SLNs (1.5%), both of which contained macrometastatic disease. Forty-seven positive nodal basins had at least one negative SLN. The hottest SLNs in these basins were negative for metastatic disease in nine cases (19.1%). In one basin (2.1%), the positive SLN count was <10% of the hottest lymph node count.Removal of lymph nodes until the bed count is 10% of the hottest lymph node will remove 98% of positive SLNs. Lymph node tumor burden influences radioactive counts.