Mucocele of the appendix is a rare entity usually mimicking an adnexal tumour. There is no specific imaging or screening method to determine the diagnosis with certainty preoperatively. Appendiceal malignancy can be the underlying cause, although it is not common. We present a case of an appendiceal mucocele mimicking an ovarian tumour by both clinical and imaging (TVS and MRI) methods. This pathological condition should be considered by all the gynaecologists in the differential diagnosis of a right-sided pelvic mass.