We described two patients (brother and sister) with familial adenomatous polyposis of the colon. It is an inherited disease with autosomal dominant pattern of inheritance. The incidence is 1:8.000, with usual onset of polyps development late in the first decade of life or during adolescence, and malignant alteration up to the fourth decade of life. APC gene located on long arm of chromosome 5 is responsible for occurrence of the disease that presents with onset of multiple adenomatous polyps in the colon (from some of them to 1000). The treatment includes chemoprevention by sulindac or aspirin that prevents or reverse process of carcinogenesis. Surgical approach is preventive colectomy up to 20 (25) years of life. APC gene mutation (deletion at codon 1309-1311) was proven by DNA analysis from blood and polyp in both patients. There was no evidence of mutations of genes p53 and K-ras. Preventive colectomy is planned as soon as possible.