A 59-year-old woman developed manifestations of Graves' disease several months after treatment with radioiodine (Na(131)) for toxic multinodular goitre. During subsequent treatment with additional radioiodine therapy Graves' ophthalmopathy developed which was severe and required treatment with prednisone and orbital radiotherapy. The literature on development of Graves' disease following Na(131) therapy is reviewed and possible pathophysiological mechanisms are discussed. In this case, possibly the first radioiodine therapy has illicited Graves' thyrotoxicosis and the subsequently added radioiodine treatments for the persistent Graves' thyrotoxicosis led to serious ophthalmopathy. Physicians should recognise Graves-like disease as a complication of Na(131)I therapy for toxic multinodular goitre and carefully consider the timing of consecutive radioiodine therapy.