Mucous cystadenomas are benign epithelial tumours with great mucous content inside. Despite being non-malignant, they acquired great size, compressing and displacing important structures and organs of the zone, with theirs unlucky outcomes. Surgical exeresis is very difficult, being almost impossible its total exeresis, showing great frequency of relapse. We present an appendix mucous cystadenoma case in a 54 years old patient.