In the Department of Radiology of the Catholic University S. Cuore in Rome, a review was made of 342 CT examinations with a view towards optimizing the therapeutic planning in patients affected by bone metastases. All patients were submitted to radiological positioning and then to CT evaluation in order to assess the volume to be treated. In 224 cases it was not necessary to perform wide CT examination (3-5 standard tomograms being enough, 2 of which at the superior and inferior margins of the planned field). In the second group of 118 patients it was necessary to perform CT (serial axial scans)--increasing by 1-1.5 cm--up to the superior and inferior margins of the lesion. The existence of 2 types of lesions was confirmed: those involving mainly bony structures and those infiltrating the soft tissues. CT evaluation allowed the definition of the target volume to the real extension of the lesion in 14% of the whole of cases, while in the group of 118 cases studied more thoroughly, the percentage went up to 41%. CT allowed a better assessment of secondary bone lesions, especially in kidney and lung neoplasms. The metastatic site that required a more frequent modification of the irradiation field was the chest. To conclude, the authors emphasize the importance of CT in assessing the target volume, especially in those cases in which conventional radiology does not allow a reliable evaluation of the lesion, possibly compromising the local monitoring of the disease.