Appendiceal carcinoma is very rare. Preoperative diagnosis of this kind of neoplasm is difficult. Even at operation in under half of cases this diagnosis is considered. We present a case of a woman admitted to the hospital with diagnosis of adnexal tumor of the right ovary. The diagnosis of adnexal mass was confirmed by ultrasound examination. Laparotomy was performed and tumor of appendix was found. There was also a small tumor (2 cm) in small bowel and some increased lymphatic nodules. Uterus with adnexis, tumor of appendix, part of small bowel and colon were resected. Because of infiltration of the neoplasm a part of the bladder was resected as well. There were no complications after operation. She received chemotherapy with 5-FU. After 9 months computed tomography revealed no changes in abdomen. Diagnosis of pelvic masses when they do not origin of adnexis is usually very difficult. In many cases proper diagnosis is made only during laparotomy.