Herein, we present the case of a 26 year old nulliparous female with a very large mucinous ovarian tumour. The patient presented at a late stage, when the cyst had accrued more than ten litres of fluid and when her abdomen was comparable to that of a term pregnancy. Radiological assessment confirmed the presence of a large cyst arising from the right ovary and occupying the whole abdomen, causing organ compression. The cyst was completely excised from the right ovary following cyst drainage with a Veress needle. Histology confirmed the lesion to be a borderline mucinous ovarian tumour, endocervical type. We discuss the case in detail, together with an update on pathogenesis and treatment of this uncommon disease.