Plummer's disease (autonomous goiter) presents a spectrum of forms, ranging from solitary autonomous thyroid nodules to numerous small autonomous areas, and from unequivocal euthyroidism to severe hyperthyroidism. Progression is often very slow, but data on long-term follow up are scarce, contradictory and limited to solitary nodules. We re-examined 58 untreated patients on one or more occasions. Follow-up time ranged from 1 to 12 years (average 4 years). There were gross clinical or scintigraphic changes in 13 patients. These included six euthyroidal patients who became (mildly) hyperthyroid, one with a change from single to numerous “hot spots,” and one in which the radionuclide disappeared in one of two separate autonomous areas. Minor changes were seen in 14 patients. Changes occurred irrespective of the scintigraphic pattern. In contrast, progression was very rapid in two of 300 other patients with the disease, leading to fatal thyrotoxic crisis within three months in one. In another patient, transient hyperthyroidism was documented after excessive iodine administration. It is concluded that patients may be left untreated as long as serious complaints and clinical suspicion of associated malignancy are absent.