Monitoring response to treatment of tumours is an increasingly important aspect of cancer radiology for several reasons. Firstly, the incidence of cancer is increasing and, furthermore, there have been major advances in treatment which have resulted in a larger number of patients surviving with treated tumours. Equally important is that there have been enormous advances in imaging over the past two decades which now permit us to obtain highly sophisticated information on tumour morphology and function using a variety of different techniques. In this review emphasis is placed on strategies for imaging in the follow-up of cancer patients and the information derived from current imaging techniques is described with particular reference to CT and MRI.