AbstractTumor progression after curative resection of gastrointestinal carcinomas is probably caused by pre‐ or intraoperative tumor cell dissemination. Disseminated tumor cells are generally detected by immunohistochemistry‐ or PCR‐based molecular‐biology methods. A consensus on which is the most adequate detection method has not yet been found, which makes the comparison of data difficult. The prognostic relevance of disseminated cells has been shown, at least in part, for esophageal, gastric, pancreatic, and colonic cancer. The data regarding hepatocellular cancer is conflicting. This article gives a critical review of tumor cell detection in gastrointestinal cancer. Semin. Surg. Oncol. 20:282–293, 2001. © 2001 Wiley‐Liss, Inc.