Gastrointestinal stromal tumors (GISTs) represent 0.1-1% of gastrointestinal malignancies. They are commonly asymptomatic and found incidentally during laparoscopy, surgical procedures or radiological studies. Diagnosis is based on histology and immunohistochemistry, while the role of imaging studies is not diagnosis-specific. We present the case of a 38-year-old patient complaining of an increase in her abdominal circumference. Consequently, a vaginal examination, a transvaginal ultrasound and an MRI of the abdomen and pelvis were carried out. It should be noted that a preoperative diagnosis of GISTs is uncommon, due to the rarity and many presentations of the disease. Ultrasound and MRI are not able to differentiate a GIST from ovarian cancer. However, if a pelvic mass is detected, the possibility of a non-gynaecological tumor has to be considered.