Symplastic leiomyoma is a rare type of leiomyoma diagnosed histologically by the presence of bizarre cells and nuclear atypia. It is difficult to diagnose preoperatively due to its overlapping clinical presentation and ultrasound features with typical leiomyomas. This paper presents a case of a 52-year-old woman who consulted due to right lower quadrant pain and abdominal enlargement. On transvaginal ultrasound and computed tomography scan, she was diagnosed with right ovarian new growth measuring 9 cm × 8 cm × 10 cm with features suggestive of an endometriotic cyst and a 16.2% risk of malignancy by the International Ovarian Tumor Analysis ADNEX model. Tumor markers CA-125 and the premenopausal ROMA were elevated. The patient underwent total abdominal hysterectomy with bilateral salpingo-oophorectomy. Intraoperatively, the right ovary appeared normal and a 10 cm retroperitoneal cystic mass was seen adherent to the right posterolateral aspect of the uterus and extending towards the right broad ligament, which exuded yellow to brown serous fluid on cut section. Histopathology revealed an intraligamentary symplastic leiomyoma with cystic degeneration. The patient was discharged stable after 3 days.