A 38-year-old woman presented with a 1-week history of low back pain, distension, weakness, and loss of appetite. Laboratory studies showed a serum CA-125 level of 281 U/ml (normal value 1.2-32 U/ml). Abdominopelvic sonography revealed massive ascites, left pleural effusion, and a heterogeneous, hypoechogenic, and smoothly outlined solid mass. The mass had a close proximity and to the anterior side of the right ovary. Doppler sonography showed that the mass was hypervascularized. Computed tomography demonstrated numerous, tortuous vascular structures around the mass and along the omentum indicating its auxiliary vascularization from the omentum. Exploratory laparotomy and histopathological examination revealed pedunculated leiomyoma with parasitized blood supply from the omentum. Ascites and pleural effusion disappeared 6 months after surgery. We present the clinical and CT features of a parasitic leiomyoma adhering to the omentum.