SUMMARY OBJECTIVES: To determine the utility of the immunehistochemistry in the detection of micrometastasis in the sentinel node dissection and the necessity to perform an axillary dissection with diagnosis of micrometastasis in the sentinel node. METHODS: We practiced the sentinel node biopsy in 130 cases in 129 patients, between 1998 and the 2004, with a follow-up average of 20 months. We used a combined technique with not filtered sulfide colloidal technetium 99 and colorant blue patent, both injected in subdermal peri areolar area. Each lymphatic node was sectioned longitudinally in fragments of 2 mm of thickness. It was made immunehistochemistry studies in the negative sentinel node. In the cases in that metastasis was diagnosed, in a second time, an axillary dissection was performed. RESULTS: We obtained a 96.92 % of identification of the sentinel nodes. In 63.49 % we only identified one sentinel node and in 36.51 % we identified more than a one sentinel node. In 28 cases, metastasic disease was reported, of which, 19 were macrometastasis disease. The immunehistochemi cal study only detected one micrometastasis case witch one, no was detected by hematoxylin and eosin stains. CONCLUSIONS: The technique of sentinel node biopsy is effective and safe for its identification. Its study in meticulous form and outside the surgical act of the breast, they highly make it recommendable for the diagnosis of micrometastasis. The study by immunehistochemistry in negative cases does not offer important benefit.