The aim of this study was to verify through relative survival (an estimate of cancer-specific survival) the true prognostic factors of colorectal cancer. The study involved 506 patients who underwent locally radical resection. All the clinical, histological and laboratory parameters were prognostically analysed for both overall and relative survival. This latter was calculated from the expected survival of the general population with identical age, sex and calendar years of observation. Univariate and multivariate analyses were applied to the proportional hazards model. Liver metastases, age, lymph node involvement and depth of bowel wall involvement were independent prognosticators of both overall and relative survival, whereas carcinoembryonic antigen (CEA) was predictive only of relative survival. Increasing age was unfavourably related to overall survival, but mildly protective with regard to relative survival. Three out of the five prognostic factors identified are the cornerstones of the current staging systems, and were confirmed as adequate by the analysis of relative survival. The results regarding age explain the conflicting findings so far obtained from studies considering overall survival only and advise against the adoption of absolute age limits in therapeutic protocols. Moreover, the prechemotherapy CEA level showed a high clinical value. British Journal of Cancer (2008) A large body of investigational data demonstrates that the prognosis of patients undergoing bowel resection for colorectal cancer is mainly determined by factors related to local tumour growth and the presence or absence of nodal and/or distant metastases. Many classification systems have been devised to categorise these anatomical factors for clinical use but an increasing number of new pathological and nonanatomical elements show interesting correlations with survival and would be worth testing systematically for selective integration into the available staging classifications. Improvement of the prognostic accuracy of these classifications might allow a more flexible use of the increasing number of new drugs and therapeutic options now available for postsurgical management of patients with colorectal cancer. However, since this malignancy is a disease of the elderly and the populations of developed countries are ageing rapidly, overall survival, as currently investigated, may not be the most suitable outcome parameter for evaluating the real prognostic impact of tumour-linked factors. Because about one-half of all colorectal carcinomas in our series occur in people aged 65 years or older, and a considerable number of these subjects die of other causes with no evidence of cancer, a fraction of these deaths should not be related to the tumour.There are two main purposes of the present work: (1) to verify the prognostic significance of the current clinicopathological factors through a study of both overall and relative survival, this latter being a selective estimate of the chance of surviving the effects of cancer; (2) to includ...