Conformal radiation therapy represents a new challenge. It offers the prospect of either increasing the radiation dose to target tissues while delivering a similar dose to organs at risk, or reducing the dose to organs at risk while maintaining the dose to target tissues. First, lymph node areas at risk are established using the available data from pathological examination. Then, based on a three-dimensional description of the anatomical regions, guidelines for the delineation of the clinical target volumes are proposed. The data presented should enable the reader to make appropriate decisions regarding the selection and delineation of the target volumes when confronted with the most frequent tumor types and sites.