Torsion of pedunculated subserosal leiomyoma of the uterus is a rare cause of acute abdomen. A 27-year-old female patient with twisted subserosal pedunculated uterine leiomyoma misdiagnosed as an adnexal mass underwent laparotomy. The patient came to the Emergency Department of General Hospital of Trikala with symptoms of acute abdomen. Primarily, clinical-laboratory examination, transabdominal ultrasound, raised the suspicion of a twisted adnexal mass. Intraoperatively, a twisted pedunculated subserosal leiomyoma of the uterus was identified and myomectomy was performed. Histological examination of the surgical specimen confirmed the diagnosis. On the third postoperative day, our patient was discharged. This paper underscores the rarity of torsion of the uterine pedunculated subserosal leiomyoma and emphasizes the necessity of urgent surgical intervention. The challenges of preoperative diagnosis are highlighted, especially when modern diagnostic imaging modalities are unavailable.