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Whereas lymph node metastases in colorectal carcinoma are an important prognostic factor, the prognostic relevance of occult tumor cells in lymph nodes is not elucidated at present. Therefore, our study intended to assess the rate of patients with occult tumor cells in histopathologically negative lymph nodes. Furthermore, we tried to evaluate an eventual influence of these occult tumor cells on patients' prognoses.For examination, we used paraffin blocks of lymph nodes, tumor-negative by conventional histopathology, from 49 patients with colorectal carcinoma (Stage I-III) after a curative (RO) tumor resection in 1987. After preparation of tissue blocks using the serial sectioning technique, the specimens were stained with the alkaline phosphatase, antialkaline phosphatase method and two monoclonal antibodies (AE1/AE3 and Ber-EP4).In 13 of 49 patients (26.5 percent), we disclosed tumor cells, mostly located in subcapsular sinuses as single cells or in groups. There was a good correlation between the detection rate and N category, tumor stage, and grading. Moreover, 33 percent of patients in Stage I/II with occult tumor cells (NO+) developed a local relapse and/or distant metastases in contrast to 12 percent of patients without tumor cells (NO−). With a median follow-up of 84 months, we found no difference in disease-free survival between the tumor cell negative and positive groups in Stage I/II patients.The results show that occult tumor cells might increase the risk for development of a local tumor relapse and/or distant metastases but do not influence patients' prognoses at all.