BACKGROUND: The recent American Joint Committee on Cancer revision of the staging system for breast cancer classifies sentinel node metastases < 0.2 mm (pN0[i+]) as node negative and those > 0.2 mm but < 2 mm are designated pN1(mi). We examined the association between size of sentinel node metastases and rate of nonsentinel node metastases, specifically in the subgroup of patients with micrometastases. STUDY DESIGN: We examined the nonsentinel nodes of 124 patients with positive sentinel nodes and correlated the likelihood of nonsentinel node involvement with the size of the metastasis in the sentinel node and primary tumor characteristics. RESULTS: Nonsentinel node metastases were found in 19% (6 of 31) of patients with sentinel node metastases ≤ 0.2 mm, 20% (6 of 30) of patients with metastases 0.2 mm to 2 mm, and 46% (29 of 63) of patients with metastases > 2 mm. Multivariate analysis found that involvement of the majority of sentinel nodes (p = 0.01) and sentinel metastases > 2 mm (p = 0.001) were significantly related to presence of metastases in nonsentinel nodes. Age, tumor size, pathology, multifocality, satellites, and lymphovascular invasion were not significantly related to nonsentinel node metastases in multivariate analysis. CONCLUSIONS: These findings indicate that frequency of nonsentinel node metastases with sentinel node metastases ≤ 0.2 mm is comparable to the frequency when sentinel metastases are > 0.2 to 2 mm. Omitting complete axillary dissection in pN1(mi) and pN0(i+) patients may leave residual disease in up to 20% of these patients.