To report a large case series of parasitic myomas and to examine their causes, associations, and risk factors.Retrospective chart review was performed on 12 patients found to have parasitic myomas between August 2000 and April 2008. The following data were systematically collected: surgery date; indications for surgery; number, dates, and types of prior surgeries; prior use of morcellation; and locations of parasitic myomas. Pathologic confirmation of all specimens was obtained.Laparoscopic evaluation confirmed the presence of intraperitoneal and retroperitoneal myomas distinct from the uterus in 12 patients. Ten of the 12 patients had prior abdominal surgery. Eight patients had prior morcellation procedures; six performed laparoscopically, two performed by laparotomy. Three patients had multiple parasitic myomas, all of whom had a history of laparoscopic myomectomy with morcellation. The majority (14 of 15) of myomas were found in the pelvis, including two retroperitoneal myomas, one of which was embedded in the bladder. Six of 15 myomas were found along the gastrointestinal tract, and 1 of 15 was found in the upper abdomen.Parasitic myomas may occur spontaneously as pedunculated subserosal myomas lose their uterine blood supply and parasitize to other organs. More parasitic myomas may be iatrogenically created after surgery, particularly surgery using morcellation techniques. With increasing rates of laparoscopic procedures, surgeons should be aware of the potential for iatrogenic parasitic myoma formation, their likely increasing frequency, and intraoperative precautions to minimize occurrence.III.