The presented case is the another one which ilustates the coexistence of cecum malignancy and genetics-conditional multisystemic arteriovenous malformations. A 64-year-old male with the mucosal form of Rendu-Osler-Weber syndrome presented a history of two different causes of lower gastrointestinal bleeding occurred clinically and confirmed by colonoscopy. The more dangerous one there was the malignant process in the cecum. The right hemicolectomy was successfully performed for malignancy removal. The postoperative course was uneventful. Repeated gastrointestinal bleedings in the course of Rendu-Osler-Weber syndrome could readily hide the developmental malignant process within the colon. The main clinical implication is the mucosal form of Rendu-Osler-Weber syndrome not excludes any malignant transformation within the gastrointestinal tract. The another one is the necessity of colonoscopy and gastroscopy in every case of gastrointestinal bleeding event.