A patient with secondary infertility, diagnosed with an endometrial polyp and right ovarian cyst, was referred for hysterolaparoscopy treatment. The woman reported no symptoms. During the hospitalisation, in addition to the aforementioned issues, left ovarian lesions and ascites were identified. A 10 cm lesion in the right ovary exhibited abundant vascularity. Tumour markers (AFP, CEA, HE4, CA-125) and the ROMA algorithm were assessed and found to be within the normal range. Laparotomy revealed a high-grade malignant tumour of unknown origin confirmed by histological examination. Uterine resection with unchanged greater omentum was performed. Immunohistochemical tests revealed positive cytokeratin (CK) reaction, including CK7 and focal CK20, as well as a marker of proliferation Ki-67 in some cells (20–30%). Signet ring cells and positive mucicarmine stain reaction were detected. The histological evaluation confirmed a Krukenberg tumour originating most likely from the stomach. The patient was referred to the Maria Skłodowska-Curie Greater Poland Cancer for further treatment.