K-ras and p53 gene mutations are known to occur in high frequencies in sporadic colorectal cancers, but findings are inconsistent in hereditary nonpolyposis colorectal cancer (HNPCC). We compared K-ras codon 12 and 13 gene mutations and p53 protein overexpression in 48 HNPCC (positive for Amsterdam criteria) and 59 sporadic colorectal adenomas, to examine whether they may represent similar or different molecular pathways to cancer. In sporadic adenomas K-ras mutations were detected in 32% and p53 overexpression in 31% of the cases. Similarly, K-ras mutations and p53 overexpression were both found in 25% of HNPCC adenomas. The frequencies of these abnormalities were not significantly different between HNPCC and sporadic adenomas. When taking differences in adenoma size into account, the frequencies were even more similar. In conclusion, these results suggest a similar molecular pathway to adenomas in HNPCC and sporadic carcinogenesis, with respect to involvement of K-ras and p53.