A randomized controlled trial was performed to compare two techniques of bilateral subtotal thyroidectomy for non-toxic nodular goitre with regard to postoperative parathyroid function. The 50 patients in group 1 underwent ligation of the trunks of the inferior thyroid arteries. In group 2 (50 patients) the branches of these arteries were suture-ligated at the thyroid capsule. Total calcium, ionized calcium and parathyroid hormone levels were determined before operation, and 6, 24 and 72 h after surgery. Ninety-one patients were seen at follow-up 5-10 months after operation. Ten patients in group 1 and 12 in group 2 required calcium and/or vitamin D supplementation for symptomatic hypocalcaemia in the immediate postoperative period. At follow-up only one patient in each group had mild hypoparathyroidism. No statistically significant differences were found between groups regarding total calcium, ionized calcium and parathyroid hormone levels. Truncal ligation of the inferior thyroid arteries during bilateral subtotal thyroidectomy does not cause hypoparathyroidism or hypocalcaemia.