Thyroids that did not show any histopathological evidence of disease were collected at necropsy from 107 patients who did not have any history of endocrine disease. Thyroid volume increases with age during childhood and adolescence, remains stable in younger adults, and declines in older subjects. There was no simple mathematical function relating thyroid volume with age: robust smooth curve fitting, however, permitted objective assessment of the age changes. The volume proportion (Vv) measurements of the various histological components did not show any important change with age, but the measurements of volume of these components reflected the gland volume changes with age. The total number of acini in the gland did not show any great age changes, and so it was concluded that the volume changes were a consequence of changes in the size of the individual acini. Measurements of internal and external surface area of the acini showed an increase in childhood and adolescence and decline in older age: unlike the other measurements reported in this paper, however, the surface area measurements must be considered as relative because of the Mandelbrot effect. The prevalence of microscopic nodules in otherwise normal thyroids increased in older patients.