A retrospective analysis of 1,826 cases (924 colon, 902 rectal) from ten institutions provided the basis of this study on the staging of cancer of the colon and rectum. The general rules of the American Joint Committee on the relationship between times and the staging of cancer have been followed. These represent modifications of the originally formulated TNM system of the Union Internationale Contre Le Cancer (UICC) which has been designed as a clinical-diagnostic classification, not applicable to cancer of inaccessible sites or structures requiring postsurgical treatment pathologic assessment of therapeutically removed specimens. Inadequacies of the clinical data requested for our study required adoption of the pTNM evaluation method of classification. Multiple regression analysis of the data demonstrated a relationship between survival and the following: depth of penetration (T), status of regional lymph nodes (N), and presence or absence of distant metastasis (M). This was similar for both sites. Basically, for the rectum it was in consonance with the original Dukes' classification (A, B, and C), and was remarkably applicable to the colon. The survival data for the two sites were so similar as to suggest the use of one set of pTNM categories not only for the postsurgical-treatment pathologic evaluation, but also for the stage grouping definitions. Strongly recommended for cancer of all sites is the development of General Oncology Data Forms to be included in the clinical charts and records of all patients with cancer.