Tumor progression following curative resection of gastrointestinal carcinomas can only be explained by pre- or intraoperative tumor cell dissemination. Disseminated tumor cells can be detected in different body compartments by using immunological or molecular biological methods. The prognostic relevance of this tumor cell detection was demonstrated in several studies. The objective of new studies should be to guide adjuvant therapy through detection of isolated disseminated tumor cells and to monitor the efficacy of adjuvant therapy by follow-up examinations.