Alterations of the p53 gene and the p53 protein are common in a wide spectrum of human malignancies. In several tumor types, p53 gene mutation and/or p53 protein overexpression correlate with a more clinically aggressive phenotype as judged by worse patient survival. This has not been clearly demonstrated to be the case in colorectal cancer. Herein, we report results of the prognostic significance of p53 protein accumulation and gene mutation in a large series of colorectal cancers (n = 541) with long patient follow-up (mean, 87 months). The large majority of patients (95%) received no postoperative systemic adjuvant therapy. The incidence of p53 accumulation detected by immunohistochemistry with the monoclonal antibody DO-7 was 30%, whereas the incidence of p53 gene mutation in exons 5-8 detected using PCR-single strand conformation polymorphism was 36%. Accumulation of p53 protein was associated with improved patient survival independent of tumor stage or grade (hazard ratio, 0.66; 95% confidence interval, 0.47-0.93; P = 0.017). A marked difference was observed depending on the location of the tumor: tumors originating in the distal colon showed a strong association between the presence of p53 accumulation and improved patient survival (P = 0.003), but this was not the case for those located in the proximal colon. Dukes' stage C tumors, but not stage B, also showed an association between p53 accumulation and better outcome (P = 0.013). Mutation of the p53 gene was associated with a trend toward improved survival, particularly in the distal tumors. Our results demonstrate that in some tumor types, the presence of p53 abnormalities can correlate with better prognosis.