Tumor recurrence following "curative" resection (= R0) of gastrointestinal cancer occurs in 30% (colorectal carcinoma) to 70% (ductal pancreatic cancer) of patients. Only colorectal cancer recurrence involves a substantial chance of a reintervention which again may result in complete cancer clearance (local recurrence 17%, metachronous liver metastases 20%, other abdominal intracavitary relapse 12%, pulmonary secondaries 17%). Five-year survival after complete re-resection approaches 40% irrespectively of the site of recurrent disease. Recognition of resectable recurrence in asymptomatic patients is based on ultrasound, endoscopy, and chest X-ray. Laboratory investigations alone, and even CEA-screening, do not suffice.