Thyroid glands were studied during surgery in 17 patients and the records of a further 53 patients who had undergone thyroidectomy were reviewed to establish the incidence of the pyramidal lobe. It was found to be present in 60 - 65% of subjects (usually being situated on the left side), and should therefore be regarded as a normal component of the thyroid gland and not as a congenital abnormality. In patients with diffuse disease of the gland the lobe is always involved.