Uterine leiomyomas are the most common type of benign tumor that occurs in the female pelvis. Uterine leiomyoma is a tumor of smooth muscles. Its prevalence is higher in the reproductive age group and decreases after menopause. Giant uterine fibroids are a rare tumor of the uterus. Giant uterine fibroids, especially subcutaneous types, are complicated by malnutrition due to deterioration of their blood supply. The complaints of the patients are non-specific: an increase in the size of the abdomen, aching pains, sometimes difficulty urinating and defecating. A physical examination reveals a giant abdominal and pelvic formation. Ultrasound with Dopplerometry and contrast-enhanced MRI diagnoses a giant tumor next to the uterus with a heterogeneous structure and the presence of cystic cavities, which is difficult to distinguish from a true large ovarian tumor. The article illustrates the complexity of differential diagnosis of giant tumor of the uterus and ovaries. There are no significant differences between these tumors during ultrasound and MRI examinations. The final diagnosis can be made intraoperativery. The article presents a clinical observation of the giant uterine fibroids of a 48-year-old female patient. Ultrasound and contrast-enhanced MRI revealed a giant tumor of the right ovary, which occupied the entire abdominal cavity, of a heterogeneous structure. Intraoperatively, two tumors, intimately adjacent to each other, 31 cm and 28 cm in diameter, emanating from the isthmus of the uterus, were found. The final diagnosis of uterine fibroids was established histologically. Difficulties in differential diagnosis between uterine fibroids and ovarian tumors before surgery are associated with the large size of the tumor and the heterogeneity of the structure due to its malnutrition.