This paper describes the methodology which can be used to determine whole-body, red marrow, blood, bladder, liver, and tumour doses delivered during 131I-mIBG therapy of neuroblastoma. The methodology is based on the Physics Protocol used in a multi-centre study undertaken by the United Kingdom Children's Cancer Study Group (UKCCSG). In this study, the estimates of the doses delivered, using 2.4-12.1 GBq 131I-mIBG, were in the following ranges: whole body, 0.14-0.65 mGy MBq-1; red marrow, 0.17-0.63 mGy MBq-1; blood, 0.04-0.17 mGy MBq-1; bladder, 2.2-5.3 mGy MBq-1; liver, 0.3-1.9 mGy MBq-1; and tumour, 0.2-16.6 mGy MBq-1.