Malignant mixed müllerian tumor (MMMT) is a rare tumor. A literature search revealed very few reports on MMMT, especially those arising in the peritoneum. We recently encountered an MMMT of primary mesenteric origin associated with left fallopian tube cancer. There have been no previous reports about its occurrence in the mesentery. When cases of peritoneal MMMT were reviewed, the disease was found to be associated with synchronous or metachronous gynecologic tumors of müllerian duct origin (ie, ovarian tumors, primary serous carcinoma of the peritoneum, fallopian tube cancer, endometrial cancer, and adenocarcinoma of the cervix) in 12 out of 32 patients (37.5%). Peritoneal MMMT are frequently associated with gynecologic tumors.