A new method for estimation of the size of the remaining tissue after thyroid resection is described. The method has been tested on cadavers and during lobectomy in a series of patients. It is shown that intraoperative quantification of the thyroid remnant can be performed mostly with +/- 0.5 g for an individual thyroid lobe with a coefficient of variation of +/- 7.6%. In patients with toxic nodular goiter and calcifications, however, the error might be larger due to the varying homogeneity of the thyroid tissue. In 73 patients with negative antibody titers operated on for hyperthyroidism it was shown that the size of the thyroid remnant was negatively correlated to the delta TSH, determined 6 weeks after the operation.