BACKGROUND Lymphatic mapping and sentinel lymph node (SN) biopsy has rapidly replaced axillary lymph node dissection for clinically node-negative breast cancers. Because of a short follow-up period when the procedure was new, there were few reports of the clinical recurrence rate in breast cancer patients treated with SN biopsy. The present study attempts to clarify the occurrence of distant failure after SN biopsy, especially in breast cancer patients with SN micrometastasis. METHODS The subjects consisted of 375 cases with clinically node-negative breast cancer, who had undergone SN biopsies. Chemotherapy and/or hormonal therapy was recommended based on the pathological primary tumor characteristics. The patients with SN micrometastasis also received adjuvant therapy equal to node-positive patients. RESULTS Examinations of lymph nodes indicated metastases in 73 cases. Among the invasive cancers, 54 cases had macrometastasis, 19 cases had micrometastasis and 241 cases had a tumor free SN. The median follow-up period ws 30 months (range 6 to 66 months). Distant relapse rates per person-years were 0.3% in the cases with tumor free SN and 3.3% among the macrometastatic cases. However, systemic disease was not observed in the cases with SN micrometastasis. CONCLUSIONS These results may show that upstaging due to SN investigation increases the number of cases who should receive anti-cancer drugs, and consequently reduces the distant relapse rate. Further studies in a large number of cases as well as longer follow-up are needed to determine the prognostic significance of SN micrometastasis.