A quantitative study of the trachea has been made in 452 children with apparently normal tracheas ranging from 28 weeks' gestation to 14 years. In the neonatal period the trachea is funnel shaped with the upper end wider than the lower end. It becomes cylindrical with increasing age. The ratio of cartilage to muscle remains constant throughout childhood. The trachea appears to grow at a greater rate, in relation to crown-rump length, during the age of 1 month to 4 years than in utero or around puberty. Normal measurements for formalin-fixed tracheas related to crown-rump length are presented.