This Safety Report provides practical guidance regarding the design and shielding of radiotherapy facilities. Methods for determining the necessary structural shielding for external beam units (cobalt-60 units, linear accelerators, superficial and orthovoltage units, and simulators), as well as for brachytherapy units, are described. Data used for determining the structural shielding necessary for all types of radiotherapy facilities are reproduced and example calculations are provided for each type of facility. In addition, specific design features that could be incorporated into radiotherapy facilities, including those related to the security of radioactive sources, are discussed. This report is intended to be used primarily by radiological physicists in the planning and design of new radiotherapy facilities and in the remodelling of existing facilities. Sections of the report will also be of interest to architects, civil engineers, hospital administrators and others who are concerned with the design of radiotherapy facilities. In addition, the guidance in the report will be useful to regulatory personnel responsible for the licensing and inspection of these facilities.