The anatomic extent of tumor (TNM, pTNM) and, in case of treatment, the residual tumor status following treatment (residual tumor, or R classification) are the strongest predictors for outcome of patients with gastrointestinal cancer. The results of the pTNM and the R classifications depend on the methods used. In particular, the pN classification correlates with the number of nodes examined. The findings of micrometastases or isolated tumor cells in bone marrow should be indicated, and such cases must be analyzed separately from other metastatic cases. The same applies to patients with positive cytology in ascites fluid or peritoneal washings without gross involvement of the peritoneum. For the R classification the additional descriptors (conv), for conventional methods used, and (soph), for sophisticated, are recommended to indicate the methods used for classification. In general, long-term survival can be expected only after R0 resection (resection without residual tumor). The observed 5-year survival after R0 resection is 15% to 40% for esophageal carcinoma, 40% to 75% for gastric carcinoma, and 55% to 60% for colorectal carcinoma; the respective figures for R1 and R2 resections are only about 5% each. In R1 and R2 cases prognosis is determined primarily by the absence or presence of distant metastases, and pT and pN are of minor significance. After R0 resection there is a wide spectrum of prognoses. Careful pTNM classification allows a good estimation of the prognosis and can be considered the gold standard for any analysis of treatment results.