OBJECTIVE Characterization of breast cancer patients with micrometastases in sentinel lymph node (SLN) and establish differences between micrometastatic breast cancers with additional metastatic lymph nodes (LNS) versus no other lymph node invasion. METHODS Analysis of 30 breast cancers, N1mi or pN0(i+), diagnosed and treated in our department from July 2000 to July 2008. RESULTS Micrometastases in SLNs were found in 30 patients. Complete axillary dissection revealed other metastatic LNs in 24%. Concerning breast cancers with additional LN invasion versus no other LN invasion, tumors located in the superior-external quadrant were more frequent in the former group. Other characteristics as clinical presentation, histological subtype, focality, cytonuclear grade, hormone receptors and Her2 expression were not significantly different in either group. Regarding SLN invasion, the presence of at least two micrometastatic foci were significantly more relevant in patients with other metastatic LN invasion (p < 0.01). Micrometastases diagnosed only after immunohistochemistry (IHC) were exclusively found in patients without other LN invasion, reaching statistical significance (p < 0.05). CONCLUSIONS Complete axillary dissection revealed additional LN invasion in 24% of patients with micrometastases in the SLN. Tumors with additional LN invasion were more frequently found in the superior external quadrant and SLNs harbored at least two micrometastatic foci. Micrometastases diagnosed exclusively by IHC techniques were more relevant in cases without additional lymph node invasion.