Borderline tumours of the ovary (BOTs) are rare tumour entities that do not show any destructive or invasive growth in the majority of cases, even though they can display characteristics of malignant tumours The mucinous subtype can also originate from the appendix, and ovarian metastases can mimic primary ovarian BOTs, often accompanied by peritoneal manifestation in terms of pseudomyxoma peritonei. In cases where a concomitant appendiceal tumour is present, it may prove difficult to determine the primary tumour. This report describes a special case of BOT with a specific example of the complexity of the differential diagnosis of pseudomyxoma peritonei. Especially the case was simultaneously linked to appendiceal and ovarian cancer. Moreover, this case was exceptional for its unusual manifestation of BOT in the cervix.