Mucinous prostate adenocarcinoma is an infrequent tumour, with no more that 50 cases described to date. This paper contributes a new case of the entity. Rather than on the rarity of the tumour, the interest in our case focuses in the unusual nature of its clinical presentation. It initially appeared as a presumable rectoanal neoplasia but the pathoanatomical examination discovered the prostatic origin of the tumoration.