Summary Diffuse astrocytomas of the adult cerebral hemispheres are unique among tumours in human beings in the extent to which their imaging features are related to histopathological characteristics and clinical behaviour. However, understanding is still restricted about the value of imaging features in the measurement of response and of progression in these tumours. The present approach used in clinical trials, which consists of an anatomical measurement of the enhancing tumour on MRI, has many problems, and might not be acceptable as a surrogate endpoint for survival in patients with glioblastoma who are enrolled in clinical trials. Dynamic imaging techniques, such as capillary permeability mapping, are being used in studies of new drugs that target specific molecular features of gliomas; however, the validity of these techniques has not been elucidated. Diffusion imaging can be valuable for fibre-tract mapping to assist surgical planning and might become useful in measuring early response to treatment in densely cellular tumours. Functional imaging techniques can be used to localise motor, sensory, and language-control areas before surgery. Intraoperative MRI has produced improvements in the extent of tumour resection, and molecular imaging is another technique on the horizon, which could come to have a role in clinical trials in the near future. Thus, as a rapidly expanding sphere of investigation, brain-tumour imaging is producing great excitement. The aim of these new techniques is to aid the identification of more effective treatments.