In a prospective study the thyroid glands of 598 healthy boys and girls (newborn to 17 years old) were examined by ultrasound. The volume of the normal gland was 1.1 cm3 in neonates, 2 cm3 in 4 year-old-children, and 8.7 cm3 in schoolchildren. The gland of a normal newborn, a girl with congenital hypothyroidism, a girl with inflammation of a median cervical cyst, a girl with insulin-dependent diabetes mellitus and autoimmune thyroiditis, and a girl with an adenoma all showed typical differences in ultrasonic structure from the normal adult gland. Sonography of the thyroid gland discloses valuable information, especially in childhood.