One hundred and twenty-two patients were reviewed 1-7 years after partial thyroidectomy for thyrotoxicosis by two surgeons who had left thyroid remnants of different size. There was no significant difference in the prevalence of hypothyroidism or in the serum levels of thyroxine, tri-iodothyronine or thyroid-stimulating hormone between the two groups of patients. The overall prevalence of hypothyroidism was 16 per cent.