A patient had both ovaries affected by clearly demarcated colliding tumour masses of different gross appearance, histological features and immunohistochemical profiles, corresponding to bilateral collision papillary serous high-grade adenocarcinoma and fibrothecoma. Despite the applied chemotherapy, it led to a lethal outcome for the patient nearly a year after the surgery. Bilateral ovarian tumours raise the question of whether they are primary tumours or metastases. Simultaneous bilateral occurrence of surface epithelial tumours with other types of ovarian tumours is rare. Therefore, it poses a great challenge in proper differential diagnostics.