L-Thyroxine was given to 3956 patients with benign goitre between 1974 and 1977, 2314 of which were controlled over a period of 3 years at regular intervals. Benign goitre in children less than 14 years old and postoperative recurrences were not evaluated. Definite reduction in goitre size wss achieved in 77.2% of patients by continuous long-term treatment over 3 years. In large goitres and those with nodular transformation the status quo was maintained in all but exceptional cases.