Whole organ step-serial section of laryngectomy specimens was carried out in 16 patients with a T3 and T4 laryngeal carcinoma to study the involvement of the thyroid gland. Three patients (19%) were found to have tumour invasion into the thyroid gland, and two patients (16%) were found to have tumour on the thyroid capsule. Of the 12 patients who had tumour involving the subglottic region, five patients were found to have involvement of the thyroid gland. Of the remaining four patients without subglottic tumour extension, none had tumour involvement of the thyroid gland. Of the five patients who had long-term survival of 10 years, two patients had subclinical hypothyroidism and one patient had clinical hypothyroidism. We recommend routine hemithyroidectomy when the subglottic region is involved by tumour. The whole thyroid gland should be preserved when the laryngeal tumour is confined to the supraglottic and glottic regions without clinical evidence of thyroid gland involvement.