Increased detection rate in the lymph nodes is seen with serial sectioning or immunohistochemistry (IHC), but the importance of occult metastases is not resolved. IHC is still not recommended in routine examination of lymph nodes. Axillary lymph nodes from 385 node-negative breast cancer patients with a median follow-up of 25 years were examined with IHC for cytokeratins, applied on routine sections. The association between classic histopathologic prognostic factors and the presence of occult metastases was evaluated. Metastases were found in 45 of 385 cases (12%), 21 metastases (47%) measured < or =0.2 mm, 8 (18%) were larger than 2 mm; 14 metastases were located in the subcapsular sinus, 22 in the parenchyma of the lymph node; and 51% (23/45) of the metastases were recognized on hematoxylin-eosin staining on "second look." The detection of metastases was significantly associated with the number of sectioned lymph nodes (6% metastases for one to five lymph nodes examined versus 17% for more than five lymph nodes) and with histologic subtype (metastases in 11% of the ductal versus 33% of the lobular carcinomas). No significant association was found between occult metastases and age, tumor size, histologic grade, estrogen or progesterone receptor status, p53, or c-erbB-2. Metastases larger than 2 mm predicted a poorer recurrence-free survival rate for the whole series. A subcapsular location of the metastases was a strong predictor of overall survival. Whether or not the metastases could be identified on hematoxylin-eosin sections did not have any prognostic significance. In the multivariate analysis, histologic grade, tumor size of the primary tumor, progesterone receptor status, and the presence of occult metastasis in the lymph nodes had a prognostic impact on survival with a 25-year follow-up.