Subtotal thyroidectomy for exophthalmic goiter is in general a remarkably successful operation. In most cases it is followed by a prompt and permanent drop in the basal metabolic rate to normal, and practically a complete disappearance of symptoms. However, in some instances the results are not so satisfactory. Either the thyrotoxicosis, although diminished, is not abolished, or else it disappears only to recur at a later date. The scarcity of accurate information in the literature with regard to the frequency, duration, types and causes of postoperative thyrotoxicosis led us to undertake the present study. It is an analysis of 190 unselected cases of exophthalmic goiter in which subtotal thyroidectomies were performed at the Massachusetts General Hospital during the six-year period from Jan. 1, 1923, to Dec. 31, 1928, and were followed by determinations of basal metabolism and clinical examinations for from three months to six years after operation.