The development and application of computerized tomography of the body have important implications in the diagnosis of tumors and in the planning of the radiotherapy treatment of malignancies because the modality provedes: a) an exact contour of transverse sections of the body; b) distinct representation of anatomic internal structures; c) ability to diagnose the presence and extent of tumor involvement of internal organs; d) opportunity to obtain, quantitatively, the "density" (x-ray absorption) of the anatomical structures in the sections; e) capability to develop isodose curves with inhomogeneity corrections; and f) ability to follow the response of a tumor to treatment, non-invasively. Although the diagnostic efficacy of computerized tomography of tumors, relative to other diagnostic modalities, is still to be defined accurately and the exact role of this new method in radiotherapy treatment planning is still to be determined, computerized tomography appears to provide oncologists with a valuable adjunct in their management of tumor patients.