Purpose: The aim of this study was to determine TP53 and NM23-H1 immunoreactivity, DNA ploidy, and S-phase fraction (SPF) in a series of 160 patients undergoing resective surgery for primary operable colorectal cancer (CRC) and to establish whether these alterations have any clinical value in predicting CRC patients' prognosis. Methods: TP53 and NM23-H1 expressions were evaluated on paraffin-embedded tissue by immunohistochemistry and DNA-ploidy and SPF on frozen tissue by flow-cytometric analysis. Results: The median follow-up time in our study group was 71 months (range 34-115 months). P53 protein expression was associated with distal tumors (P < 0.05) and DNA aneuploid tumors (P < 0.05) tumors. DNA-aneuploidy was associated with distal tumors (P < 0.01), histological grade (G3) (P < 0.05), advanced Dukes' stage (C and D) (P < 0.01), lymph node metastases (P < 0.01) and high SPF (> 18.3%) (P < 0.01). The major significant predictors for both disease relapse and death were advanced Dukes' stage, DNA-aneuploidy, and high SPF, while lymphohematic invasion was the only independent factor for relapse and non-curative resection for death. Conclusions: Our results indicate that DNA aneuploidy and high SPF are associated in CRC with a poor clinical 5-year outcome, while in contrast the prognostic role of TP53 and NM23-H1 expression is still to be clarified.