In order to establish prognostic indicators of poor clinical evolution in colorectal cancer, we have studied p53 abnormalities and K-ras mutations in 65 patients affected by colorectal carcinoma who had undergone radical surgery. A single event of p53 protein overexpression or p53 mutation, but not K-ras mutation, was significantly prevalent in recurrent tumors. A double event of K-ras mutation and p53 protein overexpression was prevalent in patients showing Dukes' stage C, but showed a lack of prevalence in patients who recurred. The presence of p53 protein overexpression does not assure an underlying mutation in colorectal carcinoma.