To investigate mutation of APC gene in sporadic colorectal tumors.Thirty-six samples of colorectal cancer and twenty-eight samples of colorectal polyps resected by operation and endoscopy were collected. As control, normal mucosal tissues in patients with cancer were taken from site 10 cm away from cancer. Three familial adenomatous polyposis (FAP) patients were also included in this study. The mutation cluster region (MCR) within exon 15 of APC gene was amplified by PCR and the PCR products were subject to SSCP analysis. Three mutant DNA fragments screned by PCR-SSCP were sequenced.No mutation in MCR of APC gene was found in normal mucosa, inflammatory polyp and hyperplastic polyp. Mutation in MCR of APC gene was found in 7 of 28 cases with sporadic colorectal polyps and in 11 of 36 cases with colorectal carcinomas. The difference in mutation frequency between adenomatous group (including FAP, 31.0%) and carcinomatous group(including FAP, 35.9%) was not statistically significant (P > 0.05). Mutation of APC gene was detected in two of three FAP patients. The same point mutation of codon 1,425 was found in both adenoma tissue and its hepatic metastasis in one FAP patient by DNA sequencing.Mutation of APC gene occurs not only in FAP, but also in sporadic colorectal tumors. It takes part in the development of most, if not all, sporadic colorectal carcinomas.