PURPOSE: A lymph node metastasis is one of most important prognostic factors of a malignancy. There is a growing interest in the role of the sentinel node (SN) in the detection of lymph node metastasis. However, the high false negative rate of a sentinel lymph node biopsy limits its utility. The aim of this study is to evaluate a micrometastasis of a gastric cancer to the histologically negative sentinel lymph nodes using the usual stains. METHODS: The SN in 44 out of 57 patients revealed no lymph node metastasis with usual hematoxylin and eosin (H&E) staining. Those nodes were embedded in paraffin and 4-micrometer-thick sections underwent, H&E staining, and cytokeratin immunohisto-chemical (IHC) staining between March 2002 and December 2002. RESULTS: Micrometastases were detected in 3 of the 44 patients without a SN metastasis. All micrometastases were detected in the patients who had metastases to the non-SN without a SN metastasis (3 of 5, 60%). Micrometastases to the SN were significantly frequent in those patients with a metastasis to the non-SN than those without a metastasis (P<0.001). From the detection of micrometastases, the sensitivity and false-negative rate of a sentinel lymph node biopsy ranged from 72.2% (13/18) to 88.9% (16/18), and from 12.8% (5/39) to 4.9% (2/41), respectively. CONCLUSION: 3 cases of micrometastasis of the SN without a metastasis were detected, and this increased the sensitivity and decreased the false negative rate of a SN biopsy. Micrometastases of the SNs were detected only in patients with a skip metastasis of the lymph nodes in this study.