Mut Y human homologue-associated polyposis is a recently described colorectal adenomatous polyposis with an autosomal recessive mode of inheritance. Several extracolonic manifestations have been reported in patients affected by Mut Y human homologue-associated polyposis (MAP). Among these, duodenal polyposis, a highly prevalent manifestation of Adenomatous Polyposis Coli related familial adenomatous polypyposis, is undoubtedly part of the clinical spectrum of the disease. The true association of other clinical manifestations with MAP remains questionable.We report the observation of two patients affected by MAP who developed an adenocarcinoma of the duodenum in the context of duodenal polyposis. These observations emphasize the malignant potential of MAP-associated duodenal polyposis and the need to enroll these patients into an upper gastrointestinal surveillance programme. Moreover, one of our patients was also diagnosed with a scapular chondrosarcoma, the other one with a high-grade astrocytoma. Although these tumours may be coincidental, we cannot rule out a real albeit rare association with MAP.