PURPOSE: Sentinel lymph node (SLN) biopsy has been shown to be accurate in axillary node staging in early breast cancer. If any SLN is positive, the standard care remains completion axillary node dissection (ALND). However over 50% of the patients with metastatic SLNs do not show other non-SLN metastasis. The purpose of this study was to identify predictors of non-SLN tumor involvement in patients with metastatic SLNs. METHODS: We reviewed 387 breast cancer patients in whom an SLN biopsy was successfully performed using a subareolar injection of 99mTc-Tin colloid. RESULTS: Among the reviewed patients, 83 patients showed positive SLNs, and subsequently underwent ALND. In 47 of 83 patients (56.6%), SLNs were the only metastatic nodes. The following factors were assessed for predictors of non- SLN metastasis: age of the patient, size, grade, histologic type, multicentricity of the primary tumor, number of SLNs removed, number of ositive SLNs, number of negative SLNs, size of the SLN metastasis, percentage of SLNs replaced by metastasis, and extracapsular extension (ECE). By multi-variate analysis, the size of SLN metastasis (<2 mm), absence of ECE, and the percent replacement (.10%) were negative predictors of non-SLN metastasis. Among 18 cases in which micrometastasis were found in the SLNs, additional metastasis in non-SLN has been found in 3 cases. This result suggests that micro-metastasis in a SLN is not a sufficient condition for not performing ALND. However, in 9 cases, in which all of three factors (micrometastasis, absence of ECE, no more than 10% replacement of SLNs by tumor cells) were present, additional metastasis had not been found in the non-SLNs. CONCLUSION: Although further study is needed to verify the result, it would seem that the presence of all three factors (micrometastasis, absence of ECE, no more than 10% replace- ment of SLNs by tumor cells) in combination might be sufficient to safely omit ALND.