Leiomyomas are common benign smooth muscle tumours of the uterus; however, extra-uterine leiomyomas are rare, particularly those arising from the round ligament. Owing to their atypical location and non-specific radiological appearance, these tumours may mimic gastrointestinal or adnexal malignancies. We report the case of a 29-year-old woman presenting with recurrent right-sided abdominal pain and a pelvic mass initially suspected to be a gastrointestinal stromal tumour (GIST) on imaging. Laparoscopic excision was performed, and histopathological examination confirmed a leiomyoma arising from the right round ligament. This case highlights the diagnostic challenges associated with round ligament leiomyomas and emphasises the importance of considering this rare entity in the differential diagnosis of pelvic masses in reproductive-aged women.