MRI is an effective tool for detection of ovarian neoplastic lesions. However, there are no highly specific radiological features that differentiate primary from metastatic ovarian masses. Histological diagnosis preoperatively is not always possible as there is a risk of disseminating an otherwise early stage primary ovarian cancer. The preoperative diagnosis of an ovarian lesion is therefore heavily dependent on the radiological features. The radiologist must rely on a combination of knowing the natural history of any known primary cancer, together with the radiological features such as bilaterality, mucinous appearance, pseudomyxoma as well as the clinical progress of the primary tumour in order to evaluate and predict the likelihood of metastatic disease. Even if a non-ovarian primary cancer is known, an ovarian mass cannot always be assumed to be a secondary lesion. Some tumours, such as BRAC-positive breast cancer, are known to have a high rate of concomitant primary ovarian cancer. Conversely, other tumours, such as gastric and appendiceal cancer, are known to have a high rate of ovarian metastatic disease. However, histology remains the only true way to determine an ovarian metastasis from a primary lesion.