Familial adenomatous polyposis (FAP) coli is an autosomal dominant syndrome characterised by germline mutations of adenomatous polyposis coli (APC) gene. A 35 years old male presented with diarrhoea on and off, pain abdomen and weight loss since one year. Upper gastroendoscopy did not reveal any focal lesion. Colonoscopy showed numerous polyps throughout the colon and an ulcerative growth in the rectum. Patient underwent distal proctocolectomy with ileostomy. Excised specimen showed adenomatous polyposis coli with one focus of invasive carcinoma in the rectum. As mentioned in the literature familial adenomatous polyposis coli (FAP) can transform to invasive adenocarcinoma which was true in our case. We present this case because of its rarity.