This case report describes a right-sided borderline ovarian tumour diagnosed unexpectedly following suspected torsion in the third trimester of pregnancy. The patient had had a right mucinous cystadenoma and left serous cystadenoma in her previous pregnancy and underwent bilateral ovarian cystectomy at the time of her first elective caesarean section. The management of borderline ovarian tumours is generally difficult in younger women of reproductive age and is made more complex by pregnancy. The authors share the challenges of managing this condition in pregnancy together with a review of the literature.