Patients with familial adenomatous polyposis coli (FAP) reveal numerous colorectal adenomas as well as benign and malignant extracolonic lesions. Adenomatous polyposis coli (APC) gene mutations are the crucial genetic defect in FAP. The APC mutation molecular analysis of 20 FAP families was performed using the novel and effective method of the heteroduplex analysis (HDA). All of these families were screened for mutations in APC exon 15. APC mutations were identified in 4 individuals of two families. These two families were also screened by the protein truncation test (PTT). The PTT results confirmed previous findings obtained by HDA. The results of molecular analysis were correlated with the clinical manifestations of extracolonic lesions and congenital hypertrophy of retinal pigment epithelium (CHRPE). Positive correlation of all clinical examinations and mutations of APC gene was observed in all 4 FAP patients.