THE size of the teeth and the rate of their development and eruption are matters of considerable importance in dental practice and attributes which we should often like to alter. Unfortunately they are characters very insusceptible to any influences which we may exert, and this applies particularly to tooth size. It is of some interest, therefore, to study a condition in which a striking abnormality of tooth size occurs, accompanied by an abnormality in the rate of development and by certain related disorders in the neighbouring tissues. Let us consider a moment what are the factors which are able to influence the size of teeth. There are genetic factors connected with family and race. Then in the direction of smallness we have the effects of radium and X-rays, certain genetic disorders affecting the mesodermal part of the tooth as in osteogenesis imperfecta and hereditary opalescent dentine, and perhaps some local inflammatory disorders such as osteomyelitis. In addition, in some forms of pituitary dwarfism of early onset the teeth may be on the small side of normal. In the direction of largeness the only suggestion of any factor other than genetic comes from the experimental work of Putnam, Teel and Benedict (1929) in which an alkaline extract of anterior pituitary gland was injected into l-weeks-old puppies. The teeth were said to be larger than in the control and though unfortunately no measurements were published some of them certainly appear so in the illustrations. Downs (1930) in a simlar experiment in which only slightly older puppies were used found no enlargement on measurement although other expected effects were obtained.As regards rate of development of the teeth and rate of eruption we know of more factors. Clinically it appears that these rates can be accelerated by additional thyroid or anterior pituitary hormone and retarded by deprivation of these substances, and there is considerable experimental support for this belief. In addition there is a striking group of cases showing dental as well as other precocity in association with hyperplasia or neoplasms of the adrenal cortex.