The authors review their experience with magnetic resonance imaging (MRI) of giant lateral ventricular tumours, placing special emphasis on the imaging features that aid in the differential diagnosis. The tumours illustrated include astrocytoma, oligodendroglioma, neurocytoma, subependymoma, metastatic lesions and subependymal giant cell astrocytoma. Because of their large size, most of these lesions cause hydrocephalus. The presence of associated edema indicates direct brain invasion or a higher grade of tumour differentiation. The degree and pattern of contrast enhancement, as well as the signal characteristics before administration of contrast agent, are nonspecific. The location of the tumour within the lateral ventricles and the patient's age are the most helpful diagnostic clues. Giant lateral ventricular tumours are uncommon, and the patients usually come to clinical attention with symptoms related to increased intracranial pressure. MRI assists in surgical planning by defining the exact location of the lesion and its relation to adjacent structures. Although the signal characteristics and patterns of contrast enhancement are nonspecific, preoperative diagnosis is possible in most cases if the imaging findings are correlated with the patient's age and the specific location of the tumour within the lateral ventricles.