We report a case of mucinous cystadenoma of uncertain malignant potential and carcinoid of appendix associated with bilateral mucinous cystadenoma of ovary and pseudomyxoma peritonei. The patient was a 46-year-old female. She suffered from dyspnea and lower abdominal palpable masses for several months. Ultrasonogram showed multilocular huge ovarian cysts. Appendectomy, transabdominal hysterectomy, bilateral salphingo-oophorectomy and biopsy of omentum were performed. The bilateral ovaries measured 16 11 cm and 7X5 cm in size, respectively. The both ovaries showed multilocular cysts filled with thick mucus material. The ovarian cysts were covered by a single layer of columnar epithelium with focal proliferation. Mucus materials dissected through the ovarian stroma (pseudomyxoma ovarii). The tip of appendix was dilated and covered by mucus material. The cut surface showed a cyst and a yellowish solid mass proximal to the cyst. Microscopically, the appendiceal cyst was lined by stratified columnar epithelium with moderate cytologic atypia. Mucus material dissected through the wall. In the proximal portion of the appendix, a classic carcinoid with focal tubular form was present in submucosa and muscle layer. The omentum was covered by thick mucus material. Microscopically, the omentum showed mucinous epithelium and mucus material (pseudomyxoma peritonei).