Radioiodine ((131)I iodide) has long been a safe, effective and widely used treatment in the management of differentiated thyroid cancer (DTC). Concerns regarding stochastic radiogenic risks have led to regulatory criteria for the release from medical confinement of patients who receive such radionuclide therapy. Over a 6-y period, the external whole-body dose rates at 1 m from 562 DTC patients were measured with an ionisation chamber calibrated in microsieverts per hour out to 5-d post-administration. Patients were stratified into four administered activity groups: 3.7 GBq (36.8 %), 5.55 GBq (47.3 %), 7.4 GBq (12.8 %) and 9.25 GBq (3 %). Consistent with previously published data, the current study demonstrated that a bi-phasic model accurately described (131)I-iodide kinetics up to at least 5-d post-administration in DTC patients, providing data that would be useful in formulating radiation safety guidelines for staff and other individuals coming into contact with such patients after treatment.