Mucocele of the appendix is uncomrnon and rarely diagnosed preoperatively. The malignant rountpart-i.e. mucinous cystadenocarcinoma--has the same grross appearance and many micro scopic features in cornmon wilhe the benign form. It rnay be associated with ovarian mucinous cystadenoma of strikingly similar microscopic appearence. A serious complication is a rupture of the mucoeele resulting in pseudomyxoma peritonei. Each case of benign and malignant mucocelr of the appendix falsely diagnosecl as an oovarian tumor before laparotxumy are presented wilh a brief rieview of the literatures.